Search backend: explicitly make gitserver a dependency of commit search
Created by: camdencheek
This moves the gitserver client onto the CommitSearch job as opposed to implicitly using the global client inside the job. This allows us to inject a mock gitserver client. As mentioned in a previous comment, I'd like to move towards passing these dependencies in at execution time rather than at planning time, but we currently follow this pattern for zoekt and searcher, so I'm maintaining consistency for now.
Test plan
Semantics preserving. Will enable easier tests.