code: public List<ConfigurationSetting> listSettings(SettingSelector options) {
          return client.listSettings(options).collectList().block();
      }
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.
  
  <p><strong>Code Samples</strong></p>
  
  <pre>
  List&lt;ConfigurationSetting&gt; settings = client.listSettings(new SettingSelector().key("prodDBConnection"));
  for (ConfigurationSetting setting : settings) {
  System.out.printf("Key: %s, Value: %s", setting.key(), setting.value());
  }</pre>
  
  @param options Optional. Options to filter configuration setting results from the service.
  @return A List of ConfigurationSettings that matches the {@code options}. If no options were provided, the List
  contains all of the current settings in the service.