ci: Add jobs running ci-fairy checks

ci: Add jobs running ci-fairy checks

These can catch various common issues in MR settings and Git commit
logs.

The "check mr" job only exists in pre-merge pipelines for MRs, and runs
automatically.

The "check commits" job only exists in pre-merge pipelines for MRs and
in pipelines for forked branches. It runs automatically in the former
case and can be manually triggered in the latter.

v2:
* Use git_archive docker image (Daniel Stone)
* Use a single sanity stage for both jobs (Tomeu Vizoso)

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6209>