Common library of RVC -> CAN functions needed so that each entity doesn't need to write its own methods

[spbrogan]

Example sending a DGN report

https://github.com/spbrogan/rvc2mqtt/blob/main/rvc2mqtt/entity/light.py#L170
https://github.com/spbrogan/rvc2mqtt/blob/main/rvc2mqtt/entity/tank_level_sensor.py#L89