## Summary
`/agents/bulk_upgrade` should return a response with a result for each agent given; including invalid or missing ids. It currently returns an empty object.

This PR includes commits from open PR elastic#95024. The additions from this PR are https://github.com/jfsiii/kibana/compare/bulk-reassign-response-should-include-all-given-agents..871ebcb

[TS type diff for response](https://github.com/jfsiii/kibana/compare/bulk-reassign-response-should-include-all-given-agents..871ebcb#diff-7006a6c170a608c8c7211fc218c0a6f4bc8ff642c170ea264db4b1b5545fb728)

```diff
- // eslint-disable-next-line @typescript-eslint/no-empty-interface
- export interface PostBulkAgentUpgradeResponse {}

+ export type PostBulkAgentUpgradeResponse = Record<
+   Agent['id'],
+   {
+     success: boolean;
+     error?: string;
+   }
+ >;
```

### Checklist

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

Co-authored-by: Kibana Machine <[email protected]>