Feature request - zones for alerts

[KM6IAU]

Users can enter an optional "zone", which would subscribe a node to alerts for said zone.

For instance, an AREDN admin for a certain area or ham club could set an alert message which would appear on the individual nodes of the users within that "zone".

Such as an alert like this: "Paxton Hill AREDN will undergo system maintenance on Jan 30 at 10am. We expect the maintenance to last 3 hours. During this time, some services will be unavailable. Questions, contact Aaron KM6IAU."

[KM6IAU]

This is implemented as "local alert", in the "advanced config".