Add a slow auto-regulation mode

[jmcollin78]

Installation with slow latency response time should have their own auto-regulation mode.
See this discu

So a new Slow auto-regulation mode have been implemented with those parameters:

    kp:float = 0.2 # 20% of the current internal regulation offset are caused by the current difference of target temperature and room temperature
    ki:float = 0.8 / 288.0 # 80% of the current internal regulation offset are caused by the average offset of the past 24 hours
    k_ext:float = 1.0 / 25.0 # this will add 1°C to the offset when it's 25°C colder outdoor than indoor
    offset_max:float = 2.0 # limit to a final offset of -2°C to +2°C
    stabilization_threshold:float = 0.0 # this needs to be disabled as otherwise the long term accumulated error will always be reset when the temp briefly crosses from/to below/above the target
    accumulated_error_threshold:float = 2.0 * 288 # this allows up to 2°C long term offset in both directions

For more information see: here

Thanks to @maia for its awesome tests and help !