CodeIndexer: Put force-push checking behind FF
What does this MR do and why?
In [Code Embeddings] Handle force pushes (#560713 - closed), we added a change in Ai::ActiveContext::Code::Indexer to check whether a new commit is due to a force-push. This force-push checking is a likely cause of Git timeout errors in other parts of Rails, see: Gitlab::Git::CommandTimedOut errors popping up ... (#568836 - closed).
In order to isolate this, we need to add the force-push checking behind a gitlab_com_derisk feature flag. In fact, this FF should have been added as part of [Code Embeddings] Handle force pushes (#560713 - closed) since Git calls are expensive, and the force-push check is not immediately needed for the initial Code Embeddings Indexing rollout.
This MR also adds logging around code that involve calls to git:
- checking if a commit is present in a git repository
- checking if a previously indexed commit is an ancestor of the latest commit
- running the
gitlab-elasticsearch-indexer, which makes "fetched changed files" calls to git
References
- Issue introducing the force-push check: [Code Embeddings] Handle force pushes (#560713 - closed)
- Feature Flag rollout issue: [FF] `active_context_code_indexer_check_force_p... (#569062 - closed)
- Bug around Git Command Timeout: Gitlab::Git::CommandTimedOut errors popping up ... (#568836 - closed)
Screenshots or screen recordings
N/A - see validation steps
How to set up and validate locally
See validation steps: !200930 (merged)
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