code: public FeatureResultInner register(String resourceProviderNamespace, String featureName) {
          return registerWithServiceResponseAsync(resourceProviderNamespace, featureName).toBlocking().single().body();
      }
docs: Registers the preview feature for the subscription.
  
  @param resourceProviderNamespace The namespace of the resource provider.
  @param featureName The name of the feature to register.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws CloudException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the FeatureResultInner object if successful.