feat (smartplugv2_energyv2): add refresh button

dp 66 is listed as read-write in issue #909 where it was introduced
from, and after experience with other devices, we now know this is not
just an indicator, but controls whether the device sends frequent updates
of sensors.

Discussion #2654

custom_components/tuya_local/devices/smartplugv2_energyv2.yaml

@@ -183,6 +183,27 @@ entities:
             value: locator
           - dps_val: "on"
             value: "on"
+  - entity: button
+    name: Refresh
+    icon: "mdi:refresh"
+    hidden: unavailable
+    category: config
+    dps:
+      - id: 66
+        type: string
+        optional: true
+        name: available
+        mapping:
+          - dps_val: null
+            value: false
+          - value: true
+      - id: 66
+        type: string
+        optional: true
+        name: button
+        mapping:
+          - dps_val: online
+            value: true
   - entity: binary_sensor
     name: Online
     class: connectivity