Add form to set service broadcast account type

Note, no option at the moment to set the service broadcast account type
as None, or back to without the broadcast permission. This has been done
for speed of development given the chance of us needing this is very
low. We can add it later if we need to.

tests/__init__.py

@@ -154,7 +154,9 @@ def service_json(
     billing_contact_email_addresses=None,
     billing_contact_names=None,
     billing_reference=None,
-    purchase_order_number=None
+    purchase_order_number=None,
+    broadcast_channel=None,
+    allowed_broadcast_provider=None,
 ):
     if users is None:
         users = []
@@ -198,6 +200,8 @@ def service_json(
         'billing_contact_names': billing_contact_names,
         'billing_reference': billing_reference,
         'purchase_order_number': purchase_order_number,
+        'broadcast_channel': broadcast_channel,
+        'allowed_broadcast_provider': allowed_broadcast_provider,
     }