Flow temperature sensors: add missing state class to enable statistics

This re-enables statistics for the flow temperature sensors (flow_in_temperature, flow_out_temperature, flow_out_temperature_target) which existed in version 2023.03.24 but is missing in the current 2023.11.30-Beta.

custom_components/luxtronik/sensor_entities_predefined.py

@@ -451,6 +451,7 @@
         device_key=DeviceKey.heating,
         entity_category=None,
         icon="mdi:waves-arrow-right",
+        state_class=SensorStateClass.MEASUREMENT,
         device_class=SensorDeviceClass.TEMPERATURE,
         native_unit_of_measurement=UnitOfTemperature.CELSIUS,
         extra_attributes=[
@@ -467,6 +468,7 @@
         device_key=DeviceKey.heating,
         entity_category=None,
         icon="mdi:waves-arrow-left",
+        state_class=SensorStateClass.MEASUREMENT,
         device_class=SensorDeviceClass.TEMPERATURE,
         native_unit_of_measurement=UnitOfTemperature.CELSIUS,
     ),
@@ -476,6 +478,7 @@
         device_key=DeviceKey.heating,
         entity_category=None,
         icon="mdi:thermometer",
+        state_class=SensorStateClass.MEASUREMENT,
         device_class=SensorDeviceClass.TEMPERATURE,
         native_unit_of_measurement=UnitOfTemperature.CELSIUS,
         extra_attributes=[