SmartplugV2 Energy: add compatible Prosto WFU-T12PM smartplug

- user proposed config was without timer, and data included suggests that the
timer dp came through later, separate from the full poll, so marked as optional.

From PR #3057

custom_components/tuya_local/devices/smartplugv2_energy.yaml

@@ -15,6 +15,9 @@ products:
   - id: uqehhcrmk5depvtl
     manufacturer: Smatrul / Beston
     model: 16A/20A / BDS01
+  - id: u8x8hhpomtchfyag
+    manufacturer: Prosto
+    model: WFU-T12PM
 entities:
   - entity: switch
     class: outlet
@@ -41,6 +44,7 @@ entities:
     dps:
       - id: 9
         type: integer
+        optional: true
         name: value
         unit: min
         range: