add DVLA organisations to API

when services are created, they'll have a dvla_org_id of 001, or
HM Government. That can be changed later using a regular update call

tests/conftest.py

@@ -75,7 +75,8 @@ def notify_db_session(notify_db):
                             "branding_type",
                             "job_status",
                             "provider_details_history",
-                            "template_process_type"]:
+                            "template_process_type",
+                            "dvla_organisation"]:
             notify_db.engine.execute(tbl.delete())
     notify_db.session.commit()