[8.x] [Security KB] Fix setup KB (elastic#201175) (elastic#201437)

# Backport

This will backport the following commits from `main` to `8.x`:
- [[Security KB] Fix setup KB
(elastic#201175)](elastic#201175)

<!--- Backport version: 9.4.3 -->

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

<!--BACKPORT [{"author":{"name":"Patryk
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KB] Fix setup KB (elastic#201175)\n\n## Summary\r\n\r\nFix an issue with
auto-recovery of Knowledge Base setup. \r\n\r\nWhen the KB setup was
initialized on an undersized cluster, the model\r\nfailed to deploy
correctly. This resulted in the KB ending up in a\r\nbroken state,
repeatedly displaying the Setup KB
button.\r\n\r\n---------\r\n\r\nCo-authored-by: kibanamachine
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KB] Fix setup KB (elastic#201175)\n\n## Summary\r\n\r\nFix an issue with
auto-recovery of Knowledge Base setup. \r\n\r\nWhen the KB setup was
initialized on an undersized cluster, the model\r\nfailed to deploy
correctly. This resulted in the KB ending up in a\r\nbroken state,
repeatedly displaying the Setup KB
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KB] Fix setup KB (elastic#201175)\n\n## Summary\r\n\r\nFix an issue with
auto-recovery of Knowledge Base setup. \r\n\r\nWhen the KB setup was
initialized on an undersized cluster, the model\r\nfailed to deploy
correctly. This resulted in the KB ending up in a\r\nbroken state,
repeatedly displaying the Setup KB
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BACKPORT-->

Co-authored-by: Patryk Kopyciński <contact@patrykkopycinski.com>

x-pack/plugins/elastic_assistant/server/ai_assistant_data_clients/knowledge_base/index.ts

@@ -178,9 +178,22 @@ export class AIAssistantKnowledgeBaseDataClient extends AIAssistantDataClient {
   public createInferenceEndpoint = async () => {
     const elserId = await this.options.getElserId();
     this.options.logger.debug(`Deploying ELSER model '${elserId}'...`);
+    const esClient = await this.options.elasticsearchClientPromise;
+
     try {
-      const esClient = await this.options.elasticsearchClientPromise;
+      await esClient.inference.delete({
+        inference_id: ASSISTANT_ELSER_INFERENCE_ID,
+        // it's being used in the mapping so we need to force delete
+        force: true,
+      });
+      this.options.logger.debug(`Deleted existing inference endpoint for ELSER model '${elserId}'`);
+    } catch (error) {
+      this.options.logger.error(
+        `Error deleting inference endpoint for ELSER model '${elserId}':\n${error}`
+      );
+    }
 
+    try {
       await esClient.inference.put({
         task_type: 'sparse_embedding',
         inference_id: ASSISTANT_ELSER_INFERENCE_ID,
@@ -198,6 +211,9 @@ export class AIAssistantKnowledgeBaseDataClient extends AIAssistantDataClient {
           task_settings: {},
         },
       });
+
+      // await for the model to be deployed
+      await this.isInferenceEndpointExists();
     } catch (error) {
       this.options.logger.error(
         `Error creating inference endpoint for ELSER model '${elserId}':\n${error}`