DRAFT: repo-aware code monitors

Created by: camdencheek

Will not be merged as-is. This is just the "put it all together to see it working." I will split this out into multiple PRs.

High level overview of how this works:

1. A new table cm_last_searched is created that stores the commit hashes that were searched as part of a code monitor search
2. Each run, we resolve the requested revisions into exact commit hashes, then exclude the previously searched commit hashes before executing the search
3. We do (2) by adding a hook to the CommitSearch job that wraps the search functionality with code-monitor-specific logic. This hook is populated by running the search job through a mapper.

Test plan