Self-managed support for Automated Merge/Squash Commit Messages

Overview

We originally built this AI feature independently of the AI Gateway (AI GW). In order to mature the feature to GA, we need it to support self-managed instances.

This is Phase 1A of using the AI GW to access LLMs. More context: AI Gateway as the Sole Access Point for Monolit... (&13024)

Proposal

Since this feature uses the existing Gitlab::Llm::Vertex::Client client, we should simply wait until groupai framework's work on Phase 1A is complete (&13397 (closed)), which should enable the feature to be routed via the AI GW.

Once &13397 (closed) is complete, we should test and verify that the feature still works as expected.