Backport !7967 and !8189 to `8-13-stable`

What does this MR do?

This backport fixes for Git 2.11 to the 8-13-stable branch so that Debian packagers can prepare a new release.

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

I've marked this as WIP since it depends on https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/120. Other than that, nothing to note.

Why was this MR needed?

From @balasankarc:

Can someone help me with backporting git 2.11 patch to 8.13.x ? How complex is it?

Our Debian native package requires it and we are going for a hard freeze tomorrow. So, I kinda need to fix it tomorrow. It would be awesome if someone could give some pointers.

Does this MR meet the acceptance criteria?

• Changelog entry added
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

/cc @balasankarc