[Manage] Add way to browse git commits and the affected pods/versions

[alloy]

This will probably be handy when dealing with claim disputes. In the manage UI I imagine:

• a simple list of commits like we have for other types and link to related PodVersions from commits/show.
• a search field where a SHA can be entered to quickly go there
• link to related commits from a pod_versions/show

Since it’s only really handy for admins, I hink we can get away with just querying the DB for all Commit records for a given git commit sha, instead of tearing the schema apart again.