Clean up docker images periodically on gitlab.archlinux.org
As we run Gitlab on docker and we always update to latest from time to time we need to clean up old unused containers.
This can be done with docker system prune -a
but then we must take special care of checking if the Gitlab container is actually running!
If we update gitlab often the priority of this issue should be raised, as it's ~ 2 GB in size for one gitlab container.
Edited by Jelle van der Waa