rsync::site dependency cleanup, part 1

rsync::site dependency cleanup, part 1

We define three things: a .service file, a .socket file, and a service.

Previously, the service would require the two files, and the .socket
file would also notify the service.  Change that to the service
subscribing to the files, so it gets a) applied after the files, and
b) refreshed if either changes.

This seems cleaner.  The net change should be that the service gets
also notified if the .service file changes.