Debian snapshots

This MR adds Debian snapshotting to yumsnapshots. In order to do that with the fewest changes possible, I got rid of the special treatment of repodata and friends. I don't really understand why rsync was being used for this in the first place, but given recent experiences there may be something I've overlooked...

You can see the output of a snapshot (just of debian and htcondor) at:

/mnt/data1/dist/tmp/ben/internal/yumsnapshot/20231108/

I configured this repo on a debian machine and it seems to work just fine, so I'm fairly confident I've gotten all the important bits.