[Obs AI Assistant] Handle Axios errors correctly (#186790)

the `kibana` function throws an axios error, and it resulted in an error
because `toJSON()` doesn't actually return a string like I expected it
to, it returns a structured object that can be converted into a string
by calling JSON.stringify().

(cherry picked from commit ca41e66)

x-pack/plugins/observability_solution/observability_ai_assistant/server/service/util/create_server_side_function_response_error.ts

@@ -6,6 +6,7 @@
  */
 
 import { errors } from '@elastic/elasticsearch';
+import { isAxiosError } from 'axios';
 import { createFunctionResponseMessage } from '../../../common/utils/create_function_response_message';
 
 export function createServerSideFunctionResponseError({
@@ -19,15 +20,18 @@ export function createServerSideFunctionResponseError({
 }) {
   const isElasticsearchError = error instanceof errors.ElasticsearchClientError;
 
-  const sanitizedError: Record<string, unknown> = JSON.parse(
-    'toJSON' in error && typeof error.toJSON === 'function' ? error.toJSON() : JSON.stringify(error)
-  );
+  const sanitizedError: Record<string, unknown> = JSON.parse(JSON.stringify(error));
 
   if (isElasticsearchError) {
     // remove meta key which is huge and noisy
     delete sanitizedError.meta;
+  } else if (isAxiosError(error)) {
+    sanitizedError.response = { message: error.response?.data?.message };
+    delete sanitizedError.config;
   }
 
+  delete sanitizedError.stack;
+
   return createFunctionResponseMessage({
     name,
     content: {