docs: def request_types(self, service_desk):
          """ Returns request types supported by a service desk instance.
          :param service_desk: The service desk instance.
          :type service_desk: ServiceDesk
          :rtype: List[RequestType]
          """
          if hasattr(service_desk, 'id'):
              service_desk = service_desk.id
          url = (self._options['server'] +
                 '/rest/servicedeskapi/servicedesk/%s/requesttype'
                 % service_desk)
          headers = {'X-ExperimentalApi': 'opt-in'}
          r_json = json_loads(self._session.get(url, headers=headers))
          request_types = [
              RequestType(self._options, self._session, raw_type_json)
              for raw_type_json in r_json['values']]
          return request_types