Revert "Remove maximum_boiler_temperature..."

This reverts commit 306a59a.

Author: bouwew

plugwise/constants.py

@@ -489,6 +489,7 @@
     "intended_central_heating_state": DATA(
         "heating_state", NONE
     ),  # This key shows in general the heating-behavior better than c-h_state. except when connected to a heatpump
+    "maximum_boiler_temperature": UOM(TEMP_CELSIUS),
     "modulation_level": UOM(PERCENTAGE),
     "return_water_temperature": DATA("return_temperature", TEMP_CELSIUS),
     # Used with the Elga heatpump - marcelveldt