code: func (req *Request) AddConfigQuery() *Request {
  	ch := req.lastChannel
  	q := &discovery.Query_ConfigQuery{
  		ConfigQuery: &discovery.ConfigQuery{},
  	}
  	req.Queries = append(req.Queries, &discovery.Query{
  		Channel: ch,
  		Query:   q,
  	})
  	req.addQueryMapping(discovery.ConfigQueryType, ch)
  	return req
  }
docs: // AddConfigQuery adds to the request a config query