codeintel: Expose commit graph metadata in GraphQL

Created by: efritz

The commit graph calculation is necessary for precise code intelligence to work correctly. We have recently had issues in customer instances due to lack of visibility into this status, and our current code intelligence integration tests are flaky because we don't have a way to check when this process has run (so we currently resort to a sleep 10 between uploading and querying, which sometimes isn't enough.

This is the first step to exposing this data to the API layer for use from the UI as well as integration testing utilities.