[8.11] [Obs AI Assistant] Use ELSER v2 (elastic#170092) (elastic#170173)

# Backport

This will backport the following commits from `main` to `8.11`:
- [[Obs AI Assistant] Use ELSER v2
(elastic#170092)](elastic#170092)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Dario
Gieselaar","email":"[email protected]"},"sourceCommit":{"committedDate":"2023-10-30T19:03:35Z","message":"[Obs
AI Assistant] Use ELSER v2 (elastic#170092)\n\nCo-authored-by: Kibana Machine
<[email protected]>","sha":"beae7b1448d00f95c3e89ccd6f62c38d5a973106","branchLabelMapping":{"^v8.12.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:enhancement","v8.11.0","v8.12.0","v8.11.1"],"number":170092,"url":"https://github.com/elastic/kibana/pull/170092","mergeCommit":{"message":"[Obs
AI Assistant] Use ELSER v2 (elastic#170092)\n\nCo-authored-by: Kibana Machine
<[email protected]>","sha":"beae7b1448d00f95c3e89ccd6f62c38d5a973106"}},"sourceBranch":"main","suggestedTargetBranches":["8.11"],"targetPullRequestStates":[{"branch":"8.11","label":"v8.11.0","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v8.12.0","labelRegex":"^v8.12.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/170092","number":170092,"mergeCommit":{"message":"[Obs
AI Assistant] Use ELSER v2 (elastic#170092)\n\nCo-authored-by: Kibana Machine
<[email protected]>","sha":"beae7b1448d00f95c3e89ccd6f62c38d5a973106"}}]}]
BACKPORT-->

Co-authored-by: Dario Gieselaar <[email protected]>

x-pack/plugins/observability_ai_assistant/server/service/index.ts

@@ -25,6 +25,8 @@ function getResourceName(resource: string) {
   return `.kibana-observability-ai-assistant-${resource}`;
 }
 
+export const ELSER_MODEL_ID = '.elser_model_2';
+
 export const INDEX_QUEUED_DOCUMENTS_TASK_ID = 'observabilityAIAssistant:indexQueuedDocumentsTask';
 
 export const INDEX_QUEUED_DOCUMENTS_TASK_TYPE = INDEX_QUEUED_DOCUMENTS_TASK_ID + 'Type';
@@ -120,6 +122,11 @@ export class ObservabilityAIAssistantService {
             auto_expand_replicas: '0-1',
             hidden: true,
           },
+          mappings: {
+            _meta: {
+              model: ELSER_MODEL_ID,
+            },
+          },
         },
       });
 
@@ -150,7 +157,7 @@ export class ObservabilityAIAssistantService {
         processors: [
           {
             inference: {
-              model_id: '.elser_model_1',
+              model_id: ELSER_MODEL_ID,
               target_field: 'ml',
               field_map: {
                 text: 'text_field',

x-pack/plugins/observability_ai_assistant/server/service/kb_service/index.ts

@@ -13,7 +13,11 @@ import type { TaskManagerStartContract } from '@kbn/task-manager-plugin/server';
 import pLimit from 'p-limit';
 import pRetry from 'p-retry';
 import { map } from 'lodash';
-import { INDEX_QUEUED_DOCUMENTS_TASK_ID, INDEX_QUEUED_DOCUMENTS_TASK_TYPE } from '..';
+import {
+  ELSER_MODEL_ID,
+  INDEX_QUEUED_DOCUMENTS_TASK_ID,
+  INDEX_QUEUED_DOCUMENTS_TASK_TYPE,
+} from '..';
 import type { KnowledgeBaseEntry } from '../../../common/types';
 import type { ObservabilityAIAssistantResourceNames } from '../types';
 import { getAccessQuery } from '../util/get_access_query';
@@ -42,8 +46,6 @@ function isAlreadyExistsError(error: Error) {
   );
 }
 
-const ELSER_MODEL_ID = '.elser_model_1';
-
 function throwKnowledgeBaseNotReady(body: any) {
   throw serverUnavailable(`Knowledge base is not ready yet`, body);
 }
@@ -199,7 +201,7 @@ export class KnowledgeBaseService {
             text_expansion: {
               'ml.tokens': {
                 model_text: text,
-                model_id: '.elser_model_1',
+                model_id: ELSER_MODEL_ID,
               },
             } as unknown as QueryDslTextExpansionQuery,
           })),