[Feature] Move MQTT client and Update to Stand-Alone Process

[patrickjaigner]

User Story As a developer, I want my edge endpoint to be available 24/7 and change the pointer to the running software version independent of the active version, so that I can keep remote control over my device.

Architecture Draft

• MQTT client is built on Paho MQTT
• OTA and RPC functionality from Thingsboard is integrated via the client
• Edge Software is built and run via Docker container
• Configuration is set via Thingsboard attributes
• The edge software and the stand-alone process communicate via SQLite
• Measurement data is persisted in a second SQLite Archive

From the workshop with @larsfroelich

[larsfroelich]

Example from thingsboard of how such a minimalistic OTA-capable paho client could look like: https://thingsboard.io/docs/user-guide/resources/firmware/mqtt_firmware_client.py

[patrickjaigner]

Configuration Concept:

• A default version-specific config is bundled into the release version
• The system-specific config is saved via ThingsBoard attributes
• While edge software startup matching keys between the default config and the system-specific config are merged with the system-specific config, overwriting the default config
• Keys not existing in the default Config are ignored
• This allows to update to a new software version with new keys that don't exist in the Thingsboard Attributes yet
• This also allows to update the ThingsBoard attributes before or after a new software update
• Processed configuration versions are persisted by the edge software in the local SQLite database with a setup timestamp. This allows the stand-alone process to check on the latest running configuration version