Feature request: Implement Pack Object cache with a hook

[sluongng]

When using goblet to serve a repository for a large concurrent CI setup, it might be desirable to make use of https://git-scm.com/docs/git-config#Documentation/git-config.txt-uploadpackpackObjectsHook to wrap around git-pack-objects and cache the output per unique request.

Multiple requests (from CI workers) asking for a same combination of objects would only trigger a single git-pack-objects which will simultaneously write to both process stdout and to an on-disk cache dir. Subsequent requests can be served from the cache dir instead of having to re-trigger git-pack-objects, which will save a lot of CPU time.

Prior art could be found in Gitlab's Gitaly https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/design_pack_objects_cache.md

[sluongng]

Let me know if you think this is something that would be beneficial to have in Goblet.

We might be interested in contributing an implementation.