Merge branch 'process-commit-worker-improvements' into 'master'

Pass commit data to ProcessCommitWorker

This changes `ProcessCommitWorker` so that it takes a Hash containing commit data instead of a commit SHA. This means the worker doesn't have to access Git just to process a commit message (and other data it may use). This in turn should solve the problem of ending up with 15 000-something jobs in the `process_commit` queue that take forever to process.

See merge request !7744