Point federationUrl to matrix-synapse container

roles/matrix-dimension/templates/config.yaml.j2

@@ -17,7 +17,7 @@ homeserver:
   # The URL that Dimension should use when trying to communicate with federated APIs on
   # the homeserver. If not supplied or left empty Dimension will try to resolve the address
   # through the normal federation process.
-  #federationUrl: "https://t2bot.io:8448"
+  federationUrl: "https://matrix-synapse:8448"
 
   # The URL that Dimension will redirect media requests to for downloading media such as
   # stickers. If not supplied or left empty Dimension will use the clientServerUrl.