Add the keep name to all housekeeper MR/commit descriptions

As suggested in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144559#note_1772656778
it would be helpful for reviewers of
[`gitlab-housekeeper`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/gems/gitlab-housekeeper)
MRs to know which specific keep generated the MR. This will make it
easier for them to locate the code and make improvements if they need
to.