Create DZ Edge Device MQTT protocol

[climategadgets]

As a DZ user, I want to have all the edge devices support the same capabilities discovery protocol, so that they can be discovered by a running DZ instance and made available for inclusion into system configuration.

Acceptance criteria:

• All currently published MQTT edge device software and firmware supports the same protocol, and is discoverable by DZ at runtime.
• Upon connecting, all devices emit a HELLO message that will allow to link further messages emitted by these devices to devices where messages originated.
  • HELLO message may contain the public key, if the firmware supports PKI, so that further messages can be signed, and control commands may be encrypted.