Add ability to change from 2 point set temperature to 1 on the fly

Creating this after discussing this on a thread in the esphome server

Currently, there's a flag that's set only when the esp32 is first connected to let home assistant know it's going to use 2 set point control.

However, it's possible a device only needs 2 set points in a specific mode and not all the time.

My thermostat for example has `heat`, `cool` and `heat_cool` modes. `heat_cool` is the only mode that requires 2 set points.

It would be nice to be able to change on the fly the ability to set 2 points and revert back to 1 when 2 is not needed. I am currently using a cloud based home assistant econet integration that can do this in home assistant. For feature parity it would be nice for esphome to support this as well.

Esphome server thread reference.


**Describe the problem you have/What new integration you would like**

**Please describe your use case for this integration and alternatives you've tried:**

**Additional context**