code: func (c *Client) SetClusterName(cn services.ClusterName) error {
  	data, err := services.GetClusterNameMarshaler().Marshal(cn)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  
  	_, err = c.PostJSON(c.Endpoint("configuration", "name"), &setClusterNameReq{ClusterName: data})
  	if err != nil {
  		return trace.Wrap(err)
  	}
  
  	return nil
  }
docs: // SetClusterName sets cluster name once, will
  // return Already Exists error if the name is already set