Add example svc to service_type (ansible#651)

https://github.com/ansible/platform-service-template/ establish a
minimal example svc that can work with the platform and we want to add
the example as a service_type

Author: TheRealHaoLiu

ansible_base/resource_registry/registry.py

@@ -97,7 +97,7 @@ def _validate_api_config(self, config):
             - Viewsets have the correct serializer, pagination and filter classes
             - Service type is set to one of awx, galaxy, eda or aap
         """
-        assert config.service_type in ["aap", "awx", "galaxy", "eda"]
+        assert config.service_type in ["aap", "awx", "galaxy", "eda", "example"]
 
     def get_resources(self):
         return self.registry