List the external proxy in fedmsg's relay_inbound.

roles/fedmsg_base/templates/relay.py.j2

@@ -35,5 +35,8 @@ config = dict(
 
         # Scripts from outside connect here (coprs, secondary arch composes)
         "tcp://busgateway01.%s:9941" % suffix,
+
+        # ...but they have to go through our external proxy first..
+        "tcp://hub.fedoraproject.org:9941",
     ],
 )