"Geo: schedule a git repack after initial clone"

What does this MR do?

Schedules a full repack after initial sync or redownload.

Are there points in the code the reviewer needs to double check?

This is slightly different than the previous tested attempts. I'm not using the simpler/faster pack-refs as we don't have it in gitaly yet.

A future alternative here will be to switch to git clone as proposed and benchmarked in https://gitlab.com/gitlab-org/gitlab-ee/issues/5447

Why was this MR needed?

When we sync using git fetch, all received refs are stored unpacked, slowing down subsequent operations.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5181 (closed)