Dual point thermostat support

[donutsoft]

Just posting here to say I've had good success with adding dual set point thermostat support in my fork at https://github.com/donutsoft/esphome-mitsubishiheatpump

There are two wins here:

1. It's set & forget. If you have a room with wild temperature swings between day & night, there's no need to switch to heating/cooling
2. If you have a multisplit, you're probably aware that all heads have to be configured to either heating or cooling otherwise everything powers down. With the separate heating/cooling setpoint, we can take advantage of the dead zone in the middle and automatically turn different heads on/off and heat/cool the remaining zones as needed.

I really think the project as a whole is suffering from all the forks that are out there, and I really don't want to be responsible for fragmenting things even further. With that being said, I'm also not sure whether you'd want to add more complexity to this project or whether you'd just want to keep it as a simple wrapper around SwiCago.

Let me know if you're interested in merging such a change, in which case I'll work on tidying up the code and start submitting pull requests.

Regards,
Paul.

[mamoit]

This would be a very good quality of life improvement for me, and provide a kind of "auto" feature to a heat pump that does not have one.
👍 for having it merged.