WHM04 doorbell: make volume optional, for Cotinse compatiblity

Cotinse doorbell is not quite compatible, as it only supports 32 tones
so product id is not attached, but since we don't have a list of the
tones it is not worth creating a new config for it.

Issue #3246

custom_components/tuya_local/devices/whm04_doorbell.yaml

@@ -93,6 +93,7 @@ entities:
             value: Alarm
       - id: 3
         type: integer
+        optional: true
         name: volume_level
         range:
           min: 0