Summary: fix(qlima_d820a_dehumidifier): make auto fan speed available as a preset

Due to this device's unnecessary complexity of using a different dp
for fan speed in purify mode, the original config only implemented the
common set of low,medium,high speeds. But in dehumidify mode, the
device also supports auto fan speed, which was inaccessible.
Duplicate the dehumidify fan speeds as preset mode so this can be accessed.

Issue #1189

custom_components/tuya_local/devices/qlima_d820a_dehumidifier.yaml

@@ -55,6 +55,21 @@ entities:
                     value: 67
                   - dps_val: high
                     value: 100
+                  - dps_val: auto
+                    value: null
+                    hidden: true
+      - id: 4
+        type: string
+        name: preset_mode
+        mapping:
+          - dps_val: auto
+            value: auto
+          - dps_val: low
+            value: low
+          - dps_val: mid
+            value: medium
+          - dps_val: high
+            value: high
       - id: 8
         type: boolean
         name: oscillate