add app_service for discord bridge

roles/synapse/templates/homeserver.yaml

@@ -1126,9 +1126,8 @@ room_prejoin_state:
 
 # A list of application service config files to use
 #
-#app_service_config_files:
+app_service_config_files:
-#  - app_service_1.yaml
+  - "/etc/matrix-synapse/discord-registration.yaml"
-#  - app_service_2.yaml
 
 # Uncomment to enable tracking of application service IP addresses. Implicitly
 # enables MAU tracking for application service users.