[8.10] [Security solution] Another GenAI response schema update (#166495

) (#166498)

# Backport

This will backport the following commits from `main` to `8.10`:
- [[Security solution] Another GenAI response schema update
(#166495)](#166495)

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

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

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solution] Another GenAI response schema update (#166495)\n\n##
Summary\r\n\r\nFollow up from
https://github.com/elastic/kibana/pull/166300\r\n\r\nWe are only using
`messages` from `choices`, so I made the other\r\n`choices` properties
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Summary\r\n\r\nFollow up from
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solution] Another GenAI response schema update (#166495)\n\n##
Summary\r\n\r\nFollow up from
https://github.com/elastic/kibana/pull/166300\r\n\r\nWe are only using
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Co-authored-by: Steph Milovic <[email protected]>

x-pack/plugins/stack_connectors/common/gen_ai/schema.ts

@@ -60,8 +60,8 @@ export const GenAiRunActionResponseSchema = schema.object(
             },
             { unknowns: 'ignore' }
           ),
-          finish_reason: schema.string(),
-          index: schema.number(),
+          finish_reason: schema.maybe(schema.string()),
+          index: schema.maybe(schema.number()),
         },
         { unknowns: 'ignore' }
       )