Bluetooth LE interface for v3

It’d be nice if there was a BLE interface to the pixelblaze v3 (given that only the ESP32 supports it) - wifi can be pretty heavyweight, but also I have a programmable BLE smartwatch (a Bangle.js 2) which seems like a perfect control interface/sensor source.

Just providing another channel for the websocket JSON interface would be okay and not too hard to implement, but since BLE is quite low bandwidth it’d also be nice to have a more thought-out set of GATT characteristics as well.