Implement support for smart grid mode

[bagbag]

With optional pcb emulation enabled, we can use smart grid mode of the heat pumps.

As this is the first time I did something with python for home assistant and only the second time I did something with python in general, I basically copied over some other entity and modified it until it worked.

The selected value is not retained in HA, only written to heishamon. So this is definitely an possible improvement to do in the future. Afaik there is no way to get the current value from heishamon (it's not even in its GUI, nor did I find something in its source code), so I guess we would have to save it in HA (or just a runtime only variable in this addon?) and hope that it's still up to date. As I don't know the best way to achieve this, I haven't bothered with it yet.

I verified this by logging it in the AQUAREA Service Cloud, where the value changes accordingly.

closes #237

[kamaradclimber]

Great patch thanks!
I've corrected types but it was exactly the right thing.

As an improvement, we could do like https://github.com/bagbag/heishamon-homeassistant/blob/main/custom_components/aquarea/definitions.py#L765-L772 which avoids to repeat the values 3 times (once in read, once in write and once in value list).