[Security Solution] AI Assistant: LLM Connector model chooser bug. New chat does not use connector's model (#199303) (#204014)

## Summary

The PR fixes [this bug](https://github.com/elastic/kibana/issues/199303)

The issue happens with some of the locally setup LLMs (like
[Ollama](https://github.com/ollama/ollama)) which requires the correct
`model` to be passed as part of the [chat completions
API](https://github.com/ollama/ollama/blob/main/docs/api.md#generate-a-chat-completion).

We had a bug in our code when on new conversation creation we would not
pass all the connectors configuration and only `connectorId` and
`actionTypeId` would be passed. Here is the old code implementation:

```
const newConversation = await createConversation({
  title: NEW_CHAT,
  ...(currentConversation?.apiConfig != null &&
  currentConversation?.apiConfig?.actionTypeId != null
    ? {
          apiConfig: {
            connectorId: currentConversation.apiConfig.connectorId,
            actionTypeId: currentConversation.apiConfig.actionTypeId,
            ...(newSystemPrompt?.id != null ? { defaultSystemPromptId: newSystemPrompt.id } : {}),
          },
        }
      : {}),
});
```

and thus the new conversation would not have the complete connector
configuration which would cause to use default model (`gpt-4o`) as a
model we pass to the LLM.

Also, I updated the default body that we use on the Test connector page,
to make sure that we send a model parameter to the LLM in case of `Open
AI > Other (OpenAI Compatible Service)` kind of connectors.

### Testing notes

Steps to reproduce:
1. Install
[Ollama](https://github.com/ollama/ollama?tab=readme-ov-file#ollama)
locally
2. Setup an OpenAI connector using Other (OpenAI Compatible Service)
provider
3. Open AI Assistant and select created Ollama connector to chat
4. Create a "New Chat"
5. The Ollama connector should be selected
6. Send a message to LLM (for example "hello world")

Expected: there should be no errors saying `ActionsClientChatOpenAI: an
error occurred while running the action - Unexpected API Error: - 404
model "gpt-4o" not found, try pulling it first`

x-pack/platform/packages/shared/kbn-elastic-assistant/impl/assistant/use_current_conversation/index.tsx

@@ -265,18 +265,24 @@ export const useCurrentConversation = ({
     }
     const newSystemPrompt = getDefaultNewSystemPrompt(allSystemPrompts);
 
+    let conversation: Partial<Conversation> = {};
+    if (currentConversation?.apiConfig) {
+      const { defaultSystemPromptId: _, ...restApiConfig } = currentConversation?.apiConfig;
+      conversation =
+        restApiConfig.actionTypeId != null
+          ? {
+              apiConfig: {
+                ...restApiConfig,
+                ...(newSystemPrompt?.id != null
+                  ? { defaultSystemPromptId: newSystemPrompt.id }
+                  : {}),
+              },
+            }
+          : {};
+    }
     const newConversation = await createConversation({
       title: NEW_CHAT,
-      ...(currentConversation?.apiConfig != null &&
-      currentConversation?.apiConfig?.actionTypeId != null
-        ? {
-            apiConfig: {
-              connectorId: currentConversation.apiConfig.connectorId,
-              actionTypeId: currentConversation.apiConfig.actionTypeId,
-              ...(newSystemPrompt?.id != null ? { defaultSystemPromptId: newSystemPrompt.id } : {}),
-            },
-          }
-        : {}),
+      ...conversation,
     });
 
     if (newConversation) {

x-pack/plugins/stack_connectors/public/connector_types/openai/constants.tsx

@@ -11,23 +11,48 @@ import { FormattedMessage } from '@kbn/i18n-react';
 import { EuiLink } from '@elastic/eui';
 import { DEFAULT_OPENAI_MODEL, OpenAiProviderType } from '../../../common/openai/constants';
 import * as i18n from './translations';
+import { Config } from './types';
 
 export const DEFAULT_URL = 'https://api.openai.com/v1/chat/completions' as const;
 export const DEFAULT_URL_AZURE =
   'https://{your-resource-name}.openai.azure.com/openai/deployments/{deployment-id}/chat/completions?api-version={api-version}' as const;
 
-export const DEFAULT_BODY = `{
+const DEFAULT_BODY = `{
     "messages": [{
         "role":"user",
         "content":"Hello world"
     }]
 }`;
-export const DEFAULT_BODY_AZURE = `{
+const DEFAULT_BODY_AZURE = `{
     "messages": [{
         "role":"user",
         "content":"Hello world"
     }]
 }`;
+const DEFAULT_BODY_OTHER = (defaultModel: string) => `{
+    "model": "${defaultModel}",
+    "messages": [{
+        "role":"user",
+        "content":"Hello world"
+    }]
+}`;
+
+export const getDefaultBody = (config?: Config) => {
+  if (!config) {
+    // default to OpenAiProviderType.OpenAi sample data
+    return DEFAULT_BODY;
+  }
+  if (config?.apiProvider === OpenAiProviderType.Other) {
+    // update sample data if Other (OpenAI Compatible Service)
+    return config.defaultModel ? DEFAULT_BODY_OTHER(config.defaultModel) : DEFAULT_BODY;
+  }
+  if (config?.apiProvider === OpenAiProviderType.AzureAi) {
+    // update sample data if AzureAi
+    return DEFAULT_BODY_AZURE;
+  }
+  // default to OpenAiProviderType.OpenAi sample data
+  return DEFAULT_BODY;
+};
 
 export const openAiConfig: ConfigFieldSchema[] = [
   {

x-pack/plugins/stack_connectors/public/connector_types/openai/params.test.tsx

@@ -9,7 +9,7 @@ import React from 'react';
 import { fireEvent, render } from '@testing-library/react';
 import ParamsFields from './params';
 import { OpenAiProviderType, SUB_ACTION } from '../../../common/openai/constants';
-import { DEFAULT_BODY, DEFAULT_BODY_AZURE, DEFAULT_URL } from './constants';
+import { DEFAULT_URL, getDefaultBody } from './constants';
 
 const messageVariables = [
   {
@@ -73,14 +73,15 @@ describe('Gen AI Params Fields renders', () => {
       );
       expect(editAction).toHaveBeenCalledTimes(2);
       expect(editAction).toHaveBeenCalledWith('subAction', SUB_ACTION.RUN, 0);
+      const body = getDefaultBody(actionConnector.config);
       if (apiProvider === OpenAiProviderType.OpenAi) {
-        expect(editAction).toHaveBeenCalledWith('subActionParams', { body: DEFAULT_BODY }, 0);
+        expect(editAction).toHaveBeenCalledWith('subActionParams', { body }, 0);
       }
       if (apiProvider === OpenAiProviderType.AzureAi) {
-        expect(editAction).toHaveBeenCalledWith('subActionParams', { body: DEFAULT_BODY_AZURE }, 0);
+        expect(editAction).toHaveBeenCalledWith('subActionParams', { body }, 0);
       }
       if (apiProvider === OpenAiProviderType.Other) {
-        expect(editAction).toHaveBeenCalledWith('subActionParams', { body: DEFAULT_BODY }, 0);
+        expect(editAction).toHaveBeenCalledWith('subActionParams', { body }, 0);
       }
     }
   );

x-pack/plugins/stack_connectors/public/connector_types/openai/params.tsx

@@ -12,8 +12,8 @@ import {
   ActionConnectorMode,
   JsonEditorWithMessageVariables,
 } from '@kbn/triggers-actions-ui-plugin/public';
-import { OpenAiProviderType, SUB_ACTION } from '../../../common/openai/constants';
-import { DEFAULT_BODY, DEFAULT_BODY_AZURE } from './constants';
+import { SUB_ACTION } from '../../../common/openai/constants';
+import { getDefaultBody } from './constants';
 import { OpenAIActionConnector, ActionParams } from './types';
 
 const ParamsFields: React.FunctionComponent<ActionParamsProps<ActionParams>> = ({
@@ -41,16 +41,10 @@ const ParamsFields: React.FunctionComponent<ActionParamsProps<ActionParams>> = (
 
   useEffect(() => {
     if (!subActionParams) {
-      // default to OpenAiProviderType.OpenAi sample data
-      let sampleBody = DEFAULT_BODY;
-
-      if (typedActionConnector?.config?.apiProvider === OpenAiProviderType.AzureAi) {
-        // update sample data if AzureAi
-        sampleBody = DEFAULT_BODY_AZURE;
-      }
+      const sampleBody = getDefaultBody(typedActionConnector?.config);
       editAction('subActionParams', { body: sampleBody }, index);
     }
-  }, [typedActionConnector?.config?.apiProvider, editAction, index, subActionParams]);
+  }, [typedActionConnector?.config, editAction, index, subActionParams]);
 
   const editSubActionParams = useCallback(
     (params: ActionParams['subActionParams']) => {

x-pack/plugins/stack_connectors/public/connector_types/openai/types.ts

@@ -18,6 +18,7 @@ export interface ActionParams {
 export interface Config {
   apiProvider: OpenAiProviderType;
   apiUrl: string;
+  defaultModel?: string;
 }
 
 export interface Secrets {