Support is a bit fragile since we don't really have a serial number to
base on. However we have a reasonnable default (source prometheus +
expression) and a way for user to specify id easily if they to change
the prometheus query.
Fixlfasci/homeassistant-prometheus-query#5
Goal is to make a first pass to allow to be exposed in the energy
dashboard.
This requires usage of HA version 2021.9 (which is beta at time of
writing) if we want to allow total_increase state_class
