Add entity registry support to media_player.snapcast (#14895)

Unique id for client is generated from prefix 'snapcast_client_'
and MAC address

Unique id for group is generated from prefix 'snapcast_group_'
and UUID provided by snapcast library

homeassistant/components/media_player/snapcast.py

@@ -104,6 +104,11 @@ class SnapcastGroupDevice(MediaPlayerDevice):
             'unknown': STATE_UNKNOWN,
         }.get(self._group.stream_status, STATE_UNKNOWN)
 
+    @property
+    def unique_id(self):
+        """Return the ID of snapcast group."""
+        return '{}{}'.format(GROUP_PREFIX, self._group.identifier)
+
     @property
     def name(self):
         """Return the name of the device."""
@@ -185,6 +190,11 @@ class SnapcastClientDevice(MediaPlayerDevice):
         client.set_callback(self.schedule_update_ha_state)
         self._client = client
 
+    @property
+    def unique_id(self):
+        """Return the ID of this snapcast client."""
+        return '{}{}'.format(CLIENT_PREFIX, self._client.identifier)
+
     @property
     def name(self):
         """Return the name of the device."""