manager: make sure we do not get stuck waiting for systemd
In some weird cases, manager can get stuck on waiting for systemd. Make sure this does not happen. If not possible, add timeout to detect these states and react accordingly.
The problem is due to races happening here (some of them are already solved by !1262 (merged)): https://gitlab.nic.cz/knot/knot-resolver/-/blob/manager/manager/knot_resolver_manager/kresd_controller/systemd/dbus_api.py#L61-108