Gitaly N+1 notice on Banzai filtering

What does this MR do?

• Adds n+1 notice for https://gitlab.com/gitlab-org/gitlab-ce/issues/43894

Are there points in the code the reviewer needs to double check?

No

Why was this MR needed?

To add the notice of https://gitlab.com/gitlab-org/gitlab-ce/issues/43894

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)