code: public Flux<ConfigurationSetting> listSettings(SettingSelector options) {
          Mono<PagedResponse<ConfigurationSetting>> result;
          if (options != null) {
              String fields = getSelectQuery(options.fields());
              result = service.listKeyValues(serviceEndpoint, options.key(), options.label(), fields, options.acceptDateTime());
          } else {
              result = service.listKeyValues(serviceEndpoint, null, null, null, null);
          }
  
          return result.flatMapMany(this::extractAndFetchConfigurationSettings);
      }
docs: Fetches the configuration settings that match the {@code options}. If {@code options} is {@code null}, then all
  the {@link ConfigurationSetting configuration settings} are fetched with their current values.
  
  @param options Optional. Options to filter configuration setting results from the service.
  @return A Flux of ConfigurationSettings that matches the {@code options}. If no options were provided, the Flux
  contains all of the current settings in the service.