Set free SMS limit depending on organisation type

Different parts of government get billed slightly differently, and
there’s differences in how much money we’re allowed to give them.

Think these numbers are right, but should be double checked.

tests/app/notify_client/test_service_api_client.py

@@ -57,6 +57,7 @@ def test_client_creates_service_with_correct_data(
     client.create_service(
         service_name='My first service',
         organisation_type='central_government',
+        free_sms_fragment_limit=2,
         message_limit=1,
         restricted=True,
         user_id=fake_uuid,
@@ -72,6 +73,7 @@ def test_client_creates_service_with_correct_data(
             name='My first service',
             # The rest pass through with the same names
             organisation_type='central_government',
+            free_sms_fragment_limit=2,
             message_limit=1,
             restricted=True,
             user_id=fake_uuid,