GitLab

During a project import, it's possible that new branches are created by
the importer to handle pull requests that have been created from forked
projects, which would increment the `pushes_since_gc` value via
`HousekeepingService.increment!` before a full garbage collection gets
to run. This causes HousekeepingService to skip the full `git gc` and
move to the incremental repack mode. To ensure that a garbage collection
is run to pack refs and objects, explicitly execute the task.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59477

Partially addresses #47424.

So that whenever we want to reserve more, we're aware,
and don't mess it up.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13766

* Rename AfterImportService
* Use constants
* Move Git operations to Gitlab::Git::Repository
* Use Regexp.union