Implement AI Gateway integration for Git Natural Language Assistant

Overview

In Phase 1A, all AI features use a single endpoint in the AI Gateway (AI GW) to access LLMs: #7549 (closed).

This is Phase 2 of using the AI GW to access LLMs. More context: AI Gateway as the Sole Access Point for Monolit... (&13024)

Proposal

• Collaborate directly with groupai framework on this work, see @oregand's message https://gitlab.com/gitlab-org/gitlab/-/issues/444274#note_1888502462:
  • "We'll begin with migrating a pilot feature(we expected this to be the vun feature/s) to this new setup and then guide each team through the process of creating and implementing their respective endpoints."
• Move Git Natural Language Assistant to use a dedicated AI GW endpoint instead of the generic endpoint.

Notes

Model used: TODO

Contacts

• Engineer DRI: @garyh
• PM (for groupcode review): @phikai
• EM (for groupcode review): @francoisrose (backend)