Report to MQTT "enter" and "leave"

[ivanvach]

Is your feature request related to a problem? Please describe.
Too many useless MQTT messages for BLE beacons. Just reducing the number is not good idea as it will reduce the granularity (in time) of the data.

Describe the solution you'd like
Provide additional "radius" attribute in the settings and send MQTT message only when a beacon "enters" or "leaves" the circle (sphere to be more accurate) with provided radius.

Describe alternatives you've considered
Keep the current raw data MQTT as an option if someone for some reason likes it, but allow such option to be disabled.

Additional context
Add any other context or screenshots about the feature request here.