Add VertexAI backend to Explain Code feature
It's behind explain_code_vertex_ai
feature flag: [Feature flag] Rollout of `explain_code_vertex_ai` (#416907 - closed). In order to test it, enable explain_code_vertex_ai
feature flag.
When the feature flag is enabled, VertexAI
model is used; otherwise, OpenAI
model is used. The input for GraphQL endpoints stays the same - it's converted to VertexAI input. The response stays the same as for OpenAI.
Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/409376+
Edited by Igor Drozdov