Move wait_for_working_tor logic from NetworkManager to systemd

As with !542 (merged) , this MR tackles 20-time.sh but doesn't kill it. It is still used to start htpdate only when we have at least started a connection to Tor.

Waiting for tor to bootstrap is moved to htpdate.service.

Since NetworkManager hooks are chained, this also impacts software upgrade. Here again, the same approach is used.

refs #18517 (closed) refs #18502 (closed)