feat: add function to read BL mac address

[felixerdy]

After starting the SenseBoxBLE, you can now read the Bluetooth Mac Address and e.g. change the name:

SenseBoxBLE::start("senseBox-BLE");
delay(1000);
String name = "senseBox:bike [" + SenseBoxBLE::getMCUId() + "]";
SenseBoxBLE::setName(name);

Which would result in the name senseBox:bike [CCF9578E439E]