Add support for a simple dual switch

There are single, three, four and six gang switches, and dual switches with
timers and other secondary entities, but no simple dual switches.

Issue #1773

custom_components/tuya_local/devices/simple_dual_switch.yaml

@@ -0,0 +1,15 @@
+name: Dual switch
+primary_entity:
+  entity: switch
+  name: Switch 1
+  dps:
+    - id: 1
+      type: boolean
+      name: switch
+secondary_entities:
+  - entity: switch
+    name: Switch 2
+    dps:
+      - id: 2
+        type: boolean
+        name: switch