Add support for refreshing synology_dsm sensors (#35141)

* Add support for refreshing synology_dsm sensors

Now supports `home_assistant.update_entity` service

* Don't immediately update sensors on add

This fixes all sensors being forcefully refreshed when setup.

homeassistant/components/synology_dsm/sensor.py

@@ -61,7 +61,7 @@ async def async_setup_entry(
                 for sensor_type in STORAGE_DISK_SENSORS
             ]
 
-    async_add_entities(sensors, True)
+    async_add_entities(sensors)
 
 
 class SynoNasSensor(Entity):
@@ -132,6 +132,10 @@ class SynoNasSensor(Entity):
         """No polling needed."""
         return False
 
+    async def async_update(self):
+        """Only used by the generic entity update service."""
+        await self._api.update()
+
     async def async_added_to_hass(self):
         """Register state update callback."""
         self._unsub_dispatcher = async_dispatcher_connect(