Add state_class into MQTT config

[johnnyfleet]

Hi there - sorry another question.

I've noticed that with the information being sent to Home assistant, the auto config is working really well, except for one thing.

I've noticed that I can't pull through temperature settings into any of the graphs in the home assistant dashboards.

Reading the documentation here it looks like the state_class property may need to be set to measurement for most of the readings.

Any guidance on how this can be achieved in the config or code for this?