Automatically run gitlabracadabra after pushing configuration updates

Extracting ideas from #17740 into dedicated issues so we can eventually close that one: run gitlabracadabra from tails/gitlab-config, e.g. in dry-run mode and then a step to manually confirm and run the deploy.

Not setting Core Work:Sysadmin for now, I'll let our sysadmins figure out whether they want this and what's the priority.