Add action attribute to Humidifier entity (#95131)

* Add HumidifierAction StrEnum

* Add action attribute to HumidifierEntity

* Update strings.json

* Add action to demo humidifier

* Add tests

* Fix imports

* Add 'off' humidifier action

* Set action to 'off' when state is 'off'

* Add 'off' action to strings.json

* Test that action sets to "off" when state is "off"

* Use is_on instead of state

* Fix typo

* black

homeassistant/components/humidifier/const.py

@@ -1,6 +1,8 @@
 """Provides the constants needed for component."""
 from enum import IntFlag
 
+from homeassistant.backports.enum import StrEnum
+
 MODE_NORMAL = "normal"
 MODE_ECO = "eco"
 MODE_AWAY = "away"
@@ -11,6 +13,17 @@ MODE_SLEEP = "sleep"
 MODE_AUTO = "auto"
 MODE_BABY = "baby"
 
+
+class HumidifierAction(StrEnum):
+    """Actions for humidifier devices."""
+
+    HUMIDIFYING = "humidifying"
+    DRYING = "drying"
+    IDLE = "idle"
+    OFF = "off"
+
+
+ATTR_ACTION = "action"
 ATTR_AVAILABLE_MODES = "available_modes"
 ATTR_CURRENT_HUMIDITY = "current_humidity"
 ATTR_HUMIDITY = "humidity"