Support setting value for valves

[tetele]

This PR introduces a simple means to use services which set numeric values in case the pwm setting of a smart thermostat is 0 and the target heater belongs to a domain which registers a value-changing entity service.

The first consequence is that the valve domain is now supported, with its set_valve_position service

This partially solves https://github.com/ScratMan/HASmartThermostat/discussions/245 i.e. you can provide a valve and just react to its position being changed.