codeintel: Add commit graph state to repo-specific uploads page

Created by: efritz

This adds a banner on the code intelligence uploads page (repo only, not the site-admin area version) that says whether or not the repository's commit graph is fresh or stale, along with the time of the last refresh.

This should help us easily debug unexpected code intelligence results which are ephemeral because of a stale commit graph (where processed uploads are not yet visible to the backend, though they appear in the UI as if they should be used).

Orthogonal efforts are being made to ensure that the commit graph update procedures are invoked as soon after an upload is processed as possible.