Device MQTT connectivity

MQTT is the communication protocol between devices and the platform. On successful authentication the device runs a mqtt client through which communicates triggered events to the platform and receives actions.

The following are the major functions of a MQTT client :-

OnConnect: Triggers when the device successfully connected to mqtt broker. This event indicates the device status is _true_ which means the device is able to communicate with the platform.

OnDisconnect: Triggers when the device disconnected form mqtt broker. This event indicates the device status id _false_ which means the device is not able to communicate with the platform.

PublishEvent: To publish messages to platform .

SubscribeAction: To receive action commands from platform.

The issue describes MQTT connectivity between devices and the platform, including connection status, publishing events, and subscribing to actions, but names no files, tests, or entry points. First identify where device authentication and MQTT handling are implemented; done should include the described connection, disconnection, publishing, and subscription behavior.

Written by the indexing model from the issue text.