[CI] Fix project build & deploy job (elastic#196562)

## Summary
In elastic#195581 we've added the option to deploy through the clickable
triggers. But in it's current state, it's broken in several aspects.

(1) It's not starting on click. Triggers was resulting in a 422 on
Buildkite's side, and after digging more into it, this was the error:
<img width="1019" alt="Screenshot 2024-10-16 at 16 53 13"
src="https://github.com/user-attachments/assets/f602dde9-2cc4-474f-b432-a3d4f9d5ae91">
Apparently, building PRs needs to be enabled on jobs that want to be
triggered through the PR bot.

(2) It is set up to run regardless of the labels

(3) There's no feedback on runs

## Changes
This PR:
 - enables buildability in the pipeline's config
 - exits early if deploy labels are missing
 - adds a comment on the PR if a deploy job is started or finished 
- removes the kibana build step, it's not needed, as we have a step to
build the docker image

TODO: 
- [x] Add feedback about a started job (either through a non-required
check, or a github comment)
 - [x] Early exit if a label is missing

There are several other builds started right now, because the logic that
would trigger a build on changing a draft to ready. To be fixed in
elastic/buildkite-pr-bot#78

Tested after manually by enabling the option on the UI, and triggering
through the checkbox:
https://buildkite.com/elastic/kibana-deploy-project-from-pr/builds/23

.buildkite/pipeline-resource-definitions/kibana-deploy-project.yml

@@ -28,9 +28,11 @@ spec:
       pipeline_file: .buildkite/pipelines/serverless_deployment/project-build-and-deploy-pr.yml
       skip_intermediate_builds: true
       provider_settings:
+        build_pull_requests: true
         prefix_pull_request_fork_branch_names: false
         skip_pull_request_builds_for_existing_commits: true
         trigger_mode: none
+      cancel_intermediate_builds: true
       teams:
         kibana-operations:
           access_level: MANAGE_BUILD_AND_READ

.buildkite/pipeline-utils/github/github.ts

@@ -93,6 +93,26 @@ export const doAnyChangesMatch = async (
   return anyFilesMatchRequired;
 };
 
+export function addComment(
+  comment: string,
+  owner = process.env.GITHUB_PR_BASE_OWNER,
+  repo = process.env.GITHUB_PR_BASE_REPO,
+  prNumber: undefined | string | number = process.env.GITHUB_PR_NUMBER
+) {
+  if (!owner || !repo || !prNumber) {
+    throw Error(
+      "Couldn't retrieve Github PR info from environment variables in order to add a comment"
+    );
+  }
+
+  return github.issues.createComment({
+    owner,
+    repo,
+    issue_number: typeof prNumber === 'number' ? prNumber : parseInt(prNumber, 10),
+    body: comment,
+  });
+}
+
 export function getGithubClient() {
   return github;
 }

.buildkite/pipelines/serverless_deployment/project-build-and-deploy-pr.yml

@@ -1,53 +1,72 @@
-agents:
-  provider: gcp
-  image: family/kibana-ubuntu-2004
-  imageProject: elastic-images-prod
+env:
+  ELASTIC_PR_COMMENTS_ENABLED: 'true'
+  GITHUB_BUILD_COMMIT_STATUS_ENABLED: 'true'
+  GITHUB_BUILD_COMMIT_STATUS_CONTEXT: kibana-deploy-project-from-pr
 
 steps:
-  - command: .buildkite/scripts/lifecycle/pre_build.sh
-    label: Pre-Build
-    timeout_in_minutes: 10
-    agents:
-      machineType: n2-standard-2
-    retry:
-      automatic:
-        - exit_status: '*'
-          limit: 1
-
-  - wait: ~
-
-  - command: .buildkite/scripts/steps/build_kibana.sh
-    label: Build Kibana Distribution and Plugins
-    agents:
-      machineType: n2-standard-16
-      preemptible: true
-    key: build
-    if: "build.env('KIBANA_BUILD_ID') == null || build.env('KIBANA_BUILD_ID') == ''"
-    timeout_in_minutes: 90
-    retry:
-      automatic:
-        - exit_status: '-1'
-          limit: 3
-
-  - wait: ~
-
-  - command: .buildkite/scripts/steps/artifacts/docker_image.sh
-    label: 'Build Project Image'
-    key: build_project_image
-    agents:
-      machineType: n2-standard-16
-      preemptible: true
-    timeout_in_minutes: 60
-    retry:
-      automatic:
-        - exit_status: '-1'
-          limit: 3
-
-  - wait: ~
-
-  - command: .buildkite/scripts/steps/serverless/deploy.sh
-    label: 'Deploy Project'
-    agents:
-      machineType: n2-standard-4
-      preemptible: true
-    timeout_in_minutes: 10
+  - group: 'Project Deployment'
+    if: "build.env('GITHUB_PR_LABELS') =~ /ci:project-deploy-(elasticsearch|observability|security)/"
+
+    steps:
+      - command: .buildkite/scripts/lifecycle/pre_build.sh
+        label: Pre-Build
+        timeout_in_minutes: 10
+        agents:
+          provider: gcp
+          image: family/kibana-ubuntu-2004
+          imageProject: elastic-images-prod
+          machineType: n2-standard-2
+        retry:
+          automatic:
+            - exit_status: '*'
+              limit: 1
+
+      - command: |
+          ts-node .buildkite/scripts/lifecycle/comment_on_pr.ts "PR Project deployment started at: $BUILDKITE_BUILD_URL"
+        label: Comment with job URL
+        agents:
+          provider: gcp
+          image: family/kibana-ubuntu-2004
+          imageProject: elastic-images-prod
+          machineType: n2-standard-2
+        timeout_in_minutes: 5
+
+      - wait: ~
+
+      - command: .buildkite/scripts/steps/artifacts/docker_image.sh
+        label: 'Build Project Image'
+        key: build_project_image
+        agents:
+          provider: gcp
+          image: family/kibana-ubuntu-2004
+          imageProject: elastic-images-prod
+          machineType: n2-standard-16
+          preemptible: true
+        timeout_in_minutes: 60
+        retry:
+          automatic:
+            - exit_status: '-1'
+              limit: 3
+
+      - wait: ~
+      - command: .buildkite/scripts/steps/serverless/deploy.sh
+        label: 'Deploy Project'
+        agents:
+          provider: gcp
+          image: family/kibana-ubuntu-2004
+          imageProject: elastic-images-prod
+          machineType: n2-standard-4
+          preemptible: true
+        timeout_in_minutes: 10
+
+      - wait: ~
+
+      - command: |
+          ts-node .buildkite/scripts/lifecycle/comment_on_pr.ts "Project deployed, see credentials at: $BUILDKITE_BUILD_URL"
+        label: Comment with job URL
+        agents:
+          provider: gcp
+          image: family/kibana-ubuntu-2004
+          imageProject: elastic-images-prod
+          machineType: n2-standard-2
+        timeout_in_minutes: 5

.buildkite/pull_requests.json

@@ -49,14 +49,15 @@
       "repoOwner": "elastic",
       "repoName": "kibana",
       "pipelineSlug": "kibana-deploy-project-from-pr",
-
+      "skip_ci_labels": [],
       "enabled": true,
       "allow_org_users": true,
       "allowed_repo_permissions": ["admin", "write"],
       "allowed_list": ["elastic-vault-github-plugin-prod[bot]"],
-      "set_commit_status": false,
+      "set_commit_status": true,
+      "commit_status_context": "kibana-deploy-project-from-pr",
       "build_on_commit": false,
-      "build_on_comment": false,
+      "build_on_comment": true,
       "build_drafts": false,
       "trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:deploy)\\W+(?:project))$",
       "kibana_versions_check": true,

.buildkite/scripts/lifecycle/comment_on_pr.ts

@@ -0,0 +1,64 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { addComment } from '#pipeline-utils';
+
+const ALLOWED_ENV_VARS = [
+  'BUILDKITE_BRANCH',
+  'BUILDKITE_BUILD_ID',
+  'BUILDKITE_BUILD_NUMBER',
+  'BUILDKITE_BUILD_URL',
+  'BUILDKITE_COMMIT',
+  'BUILDKITE_PIPELINE_NAME',
+  'BUILDKITE_PIPELINE_SLUG',
+  'GITHUB_PR_BASE_OWNER',
+  'GITHUB_PR_BASE_REPO',
+  'GITHUB_PR_BRANCH',
+  'GITHUB_PR_HEAD_SHA',
+  'GITHUB_PR_HEAD_USER',
+  'GITHUB_PR_LABELS',
+  'GITHUB_PR_NUMBER',
+  'GITHUB_PR_OWNER',
+  'GITHUB_PR_REPO',
+  'GITHUB_PR_TARGET_BRANCH',
+  'GITHUB_PR_TRIGGERED_SHA',
+  'GITHUB_PR_TRIGGER_USER',
+  'GITHUB_PR_USER',
+];
+const DEFAULT_MESSAGE_TEMPLATE =
+  '🚀 Buildkite job started for PR #${GITHUB_PR_NUMBER}: ${BUILDKITE_BUILD_URL}';
+
+export function commentOnPR() {
+  const messageTemplate =
+    process.argv.slice(2)?.join(' ') ||
+    process.env.JOB_START_COMMENT_TEMPLATE ||
+    DEFAULT_MESSAGE_TEMPLATE;
+  if (messageTemplate === DEFAULT_MESSAGE_TEMPLATE) {
+    console.log('No message template provided, using default message');
+  } else {
+    console.log(`Using message template: ${messageTemplate}`);
+  }
+
+  const message = messageTemplate.replace(/\${([^}]+)}/g, (_, envVar) => {
+    if (ALLOWED_ENV_VARS.includes(envVar)) {
+      return process.env[envVar] || '';
+    } else {
+      return '${' + envVar + '}';
+    }
+  });
+
+  return addComment(message);
+}
+
+if (require.main === module) {
+  commentOnPR().catch((error) => {
+    console.error(error);
+    process.exit(1);
+  });
+}