feat (loonas_curtain): improve compatibility

Make position optional, to improve compatibility with an unknown
matching curtain motor. Add its product id, in case the dps returned
are even more erratic, so at least it still matches in cloud assisted setup.

Issue #3872

custom_components/tuya_local/devices/loonas_curtain.yaml

@@ -10,6 +10,8 @@ products:
   - id: dpqsvdbi
     manufacturer: Miju
     model: CM82
+  - id: paxwqamvmc4hpebp
+    name: Curtain motor
 entities:
   - entity: cover
     class: curtain
@@ -28,6 +30,7 @@ entities:
       - id: 2
         name: position
         type: integer
+        optional: true
         range:
           min: 0
           max: 100