add webhook URL to custom trigger dialog

endpoints/trigger.py

@@ -621,6 +621,7 @@ class CustomBuildTrigger(BuildTrigger):
     return dockerfile_id, tags, build_name, trigger.config['subdir'], metadata
 
   def activate(self, trigger_uuid, standard_webhook_url, auth_token, config):
+    config['webhook_url'] = standard_webhook_url
     config['public_key'], private_key = generate_ssh_keypair()
     return config, private_key