Revert "Revert "re-enable kme pipeline for testing (#171451)"" (#171694)

I pushed this revert up initially via
e79ca5e while debugging an issue with
CI waiting for agents. This was not the root cause and can be
unreverted.

.buildkite/pull_requests.json

@@ -55,14 +55,14 @@
       "repoName": "kibana",
       "pipelineSlug": "kibana-kme-test",
 
-      "enabled": false,
+      "enabled": true,
       "allow_org_users": true,
       "allowed_repo_permissions": ["admin", "write"],
       "allowed_list": ["barlowm", "renovate[bot]"],
       "set_commit_status": true,
-      "commit_status_context": "kibana-ci",
+      "commit_status_context": "kibana-ci-test",
       "build_on_commit": true,
-      "build_on_comment": true,
+      "build_on_comment": false,
       "trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:build|test)\\W+(?:this|it))",
       "always_trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:build|test)\\W+(?:this|it))",
       "skip_ci_labels": [],