Sunbeam dual bed warmer: preheat A also needs to be optional

Caution: there are only 3 non-optional dps left now, this may be a problematic
device that randomly has various dps missing, so at some point we need to
draw a line and tell users they need to play around with settings until they
can get it added.

Issue #2249

custom_components/tuya_local/devices/sunbeam_dual_bedwarmer.yaml

@@ -179,6 +179,7 @@ secondary_entities:
     dps:
       - id: 24
         type: boolean
+        optional: true
         name: switch
   - entity: switch
     name: Preheat B