Panel connection status
It would be nice to add a topic to indicate whether PAI is currently connected to the panel.

## Feature description
In my case, connecting with IP150, if IP150 becomes unreachable and PAI cannot connect to it, there's no indication of a failure.
All the sensors show online, paradox/interface/MQTTInterface is also online.
A new sensor similar to paradox/interface/MQTTInterface would be helpful to indicate that the panel is currently online.