Pass though file_url from extended data attrs (#17801)

* pass though file_url from extended data attrs so synology chat bot can send files

* some code cleanup

homeassistant/components/notify/synology_chat.py

@@ -11,10 +11,11 @@ import requests
 import voluptuous as vol
 
 from homeassistant.components.notify import (
-    BaseNotificationService, PLATFORM_SCHEMA)
+    BaseNotificationService, PLATFORM_SCHEMA, ATTR_DATA)
 from homeassistant.const import CONF_RESOURCE
 import homeassistant.helpers.config_validation as cv
 
+ATTR_FILE_URL = 'file_url'
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
     vol.Required(CONF_RESOURCE): cv.url,
@@ -43,6 +44,12 @@ class SynologyChatNotificationService(BaseNotificationService):
             'text': message
         }
 
+        extended_data = kwargs.get(ATTR_DATA)
+        file_url = extended_data.get(ATTR_FILE_URL) if extended_data else None
+
+        if file_url:
+            data['file_url'] = file_url
+
         to_send = 'payload={}'.format(json.dumps(data))
 
         response = requests.post(self._resource, data=to_send, timeout=10)