feat(shell): add mqtt + env config support

[ahochsteger]

This PR adds support for MQTT (read-only) and configuration using environment variables to the Wattpilot Shell.

MQTT Support

It is possible to publish JSON messages received from Wattpilot and/or individual property value changes to an MQTT server.
The easiest way to start the shell with MQTT support is using these environment variables:

export MQTT_ENABLED=true
export MQTT_HOST=<mqtt_host>
export WATTPILOT_HOST=<wattpilot_ip>
export WATTPILOT_PASSWORD=<wattpilot_password>
python3 shell.py

Environment Variables

Environment Variable	Description	Default Value
MQTT_BASE_TOPIC	Base topic for MQTT	wattpilot
MQTT_CLIENT_ID	MQTT client ID	wattpilot2mqtt
MQTT_ENABLED	Enable MQTT	false
MQTT_HA_DISCOVERY_ENABLED	Enable Home Assistant Discovery (not yet implemented)	false
MQTT_HOST	MQTT host to connect to
MQTT_MESSAGE_TOPIC_PATTERN	Topic pattern to publish Wattpilot messages to	{baseTopic}/{serialNumber}/messages/{messageType}
MQTT_PORT	Port of the MQTT host to connect to	1883
MQTT_PROPERTY_READ_TOPIC_PATTERN	Topic pattern to publish property values to	{baseTopic}/{serialNumber}/properties/{propName}
MQTT_PROPERTY_SET_TOPIC_PATTERN	Topic pattern to listen for property value changes for (not yet implemented)	{baseTopic}/{serialNumber}/properties/{propName}/set
MQTT_PUBLISH_MESSAGES	Publish received Wattpilot messages to MQTT	true
MQTT_PUBLISH_PROPERTIES	Publish received property values to MQTT	false
MQTT_WATCH_PROPERTIES	List of space-separated default properties to publish changes for (use "" for all properties)	amp car fna lmo sse
WATTPILOT_CONNECT_TIMEOUT	Connect timeout for Wattpilot connection	30
WATTPILOT_DEBUG_LEVEL	Debug level	INFO
WATTPILOT_INITIALIZED_TIMEOUT	Wait timeout for property initialization	30
WATTPILOT_HOST	IP address of the Wattpilot device to connect to
WATTPILOT_PASSWORD	Password for connecting to the Wattpilot device

[joscha82]

Thanks, i will add the dependency for paho mqtt client later this day to setup.py before generating a pypi package for #3