Allow clear_integral service to set a non zero value

[shardshunt]

This change extends the existing clear_integral service so the PID integral term can be reset to an arbitrary value instead of always being forced to zero. When no value is provided, the integral is still cleared to 0.

In some cases the integral term may be known or calculable to be close to the correct steady state value. Allowing it to be restored or deliberately biased makes it possible to slow integral action and reduce overshoot after mode changes, restarts, or manual intervention.

Example of usage:

action: smart_thermostat.clear_integral
data:
  value: 10
target:
  entity_id: climate.controller_name