Add night arm mode to MQTT alarm control panel (#8471)

source/_components/alarm_control_panel.mqtt.markdown

@@ -20,6 +20,7 @@ The component will accept the following states from your Alarm Panel (in lower c
 - `disarmed`
 - `armed_home`
 - `armed_away`
+- 'armed_night'
 - `pending`
 - `triggered`
 
@@ -75,6 +76,11 @@ payload_arm_away:
   required: false
   type: string
   default: ARM_AWAY
+payload_arm_night:
+  description: The payload to set armed-night mode on your Alarm Panel.
+  required: false
+  type: string
+  default: ARM_NIGHT
 code:
   description: If defined, specifies a code to enable or disable the alarm in the frontend.
   required: false