code: public RequestConfig with(Heroku.RequestKey key, Map<Heroku.RequestKey, Either> value) {
          RequestConfig newConfig = copy();
          newConfig.config.put(key, new Either(value));
          return newConfig;
      }
docs: Sets a {@link com.heroku.api.Heroku.RequestKey} parameter.
  @param key Heroku request key
  @param value value of the property
  @return A new {@link RequestConfig}