Update JSON schema postage validation for new values

tests/app/service/test_rest.py

@@ -2340,7 +2340,8 @@ def test_create_pdf_letter(mocker, sample_service_full_permissions, client, fake
         {"postage": "third", "filename": "string", "created_by": "string", "file_id": "string",
          "recipient_address": "Some Address"},
         [
-            {'error': 'ValidationError', 'message': 'postage invalid. It must be either first or second.'}
+            {'error': 'ValidationError',
+             'message': 'postage invalid. It must be first, second, europe or rest-of-world.'}
         ]
     )
 ])

tests/app/template/test_rest.py

@@ -794,7 +794,8 @@ def test_create_a_template_with_foreign_service_reply_to(admin_request, sample_u
         {"name": "my template", "template_type": "sms", "content": "hi", "postage": "third",
          "service": "1af43c02-b5a8-4923-ad7f-5279b75ff2d0", "created_by": "30587644-9083-44d8-a114-98887f07f1e3"},
         [
-            {"error": "ValidationError", "message": "postage invalid. It must be either first or second."},
+            {"error": "ValidationError",
+             "message": "postage invalid. It must be first, second, europe or rest-of-world."},
         ]
     ),
 ])

tests/app/v2/notifications/test_post_letter_notifications.py

@@ -637,7 +637,7 @@ def test_post_letter_notification_throws_error_for_invalid_postage(client, notif
 
     assert response.status_code == 400, response.get_data(as_text=True)
     resp_json = json.loads(response.get_data(as_text=True))
-    assert resp_json['errors'][0]['message'] == "postage invalid. It must be either first or second."
+    assert resp_json['errors'][0]['message'] == "postage invalid. It must be first, second, europe or rest-of-world."
 
     assert not Notification.query.first()