codeintel: Add repository summary resolvers

Created by: efritz

This PR adds additional resolvers to help determine a repo state w.r.t. code intelligence. These resolvers add ways to get timestamps of last activity for auto-indexing and upload expiration scans, as well as a summary of upload and index records for each unique index/root pair. This will let us see if a particular portion of a repo is currently or consistently failing.

This PR is currently blocking progress on badge work in #33153.

Test plan

Additional unit tests in the PR.