fix(holman_wx4_taptimer): make overall "Manual timers" available

Since the device does not readily report the value of the
manual timers dp, we cannot set individual timers.

Make the full value available as a text entity (hidden
by default) to allow initialising it to a known value as
a workaround for the poor device behaviour.

Issue #6107

custom_components/tuya_local/devices/holman_wx4_taptimer.yaml

@@ -806,6 +806,16 @@ entities:
         mask: "00000000000000ff"
         optional: true
         name: remaining_min
+  - entity: text
+    name: Manual timers
+    category: config
+    icon: "mdi:timer"
+    hidden: true
+    dps:
+      - id: 172
+        type: base64
+        optional: true
+        name: value
   - entity: text
     name: Timer delays
     category: config