Obtain the new descriptors and network status documents by signals instead of every hour

The network status and descriptors are obtained every hour https://gitlab.torproject.org/tpo/network-health/sbws/-/blob/maint-1.1/sbws/lib/relaylist.py#L308.

Torflow obtain them as they come.

It could be done with stem using:

controller.add_event_listener(
            listener_fn, EventType.NS, EventType.NEWDESC)

Also, instead overwriting those values, Relay could have a dictionary (key would be the timestamp) with a subset of the attributes of document, in case we might need to calculate median/mean of those attributes

Edit: fix typo, fix that it was changed to 1h, not 5min and actual link to the code.