Add operator channel to broadcast settings route

Looks identical to the government channel in terms of the interface

app/service/service_broadcast_settings_schema.py

@@ -4,7 +4,7 @@ service_broadcast_settings_schema = {
     "type": "object",
     "title": "Set a services broadcast settings",
     "properties": {
-        "broadcast_channel": {"enum": ["test", "severe", "government"]},
+        "broadcast_channel": {"enum": ["operator", "test", "severe", "government"]},
         "service_mode": {"enum": ["training", "live"]},
         "provider_restriction": {"enum": ["three", "o2", "vodafone", "ee", "all"]}
     },