Add service versioning to broadcast account type change

We are using the `set_broadcast_service_type` route to make changes to
service objects. However, we had forgotten to add the `version_class`
decorator to it which will mean the changing of a service going from
training to live mode will also be recorded in the services_history
table for free. Whilst not essential, this easy change makes things more
consistent for how we update other services.

app/dao/broadcast_service_dao.py

@@ -3,11 +3,19 @@ from datetime import datetime
 from flask import current_app
 
 from app import db
-from app.models import ServiceBroadcastSettings, ServicePermission, Organisation, BROADCAST_TYPE, EMAIL_AUTH_TYPE
-from app.dao.dao_utils import transactional
+from app.dao.dao_utils import transactional, version_class
+from app.models import (
+    Service,
+    ServiceBroadcastSettings,
+    ServicePermission,
+    Organisation,
+    BROADCAST_TYPE,
+    EMAIL_AUTH_TYPE
+)
 
 
 @transactional
+@version_class(Service)
 def set_broadcast_service_type(service, service_mode, broadcast_channel, provider_restriction):
     insert_or_update_service_broadcast_settings(
         service, channel=broadcast_channel, provider_restriction=provider_restriction