This script sends the current status of the device on a MQTT topic.
It can be run either in a docker container or as a systemd service.
Three different states are detected: Online, Offline or Crashed, the which are also the default messages.
Crashes are 'detected' by setting a last will message.
Additionally the start time of the device is sent.
The script can be configured either via a configuration file (recommended when running as a service) or via environment variables (for docker containers), a template .env is provided.