docs: @BetaApi
    public final Operation addSignedUrlKeyBackendBucket(
        ProjectGlobalBackendBucketName backendBucket, SignedUrlKey signedUrlKeyResource) {
  
      AddSignedUrlKeyBackendBucketHttpRequest request =
          AddSignedUrlKeyBackendBucketHttpRequest.newBuilder()
              .setBackendBucket(backendBucket == null ? null : backendBucket.toString())
              .setSignedUrlKeyResource(signedUrlKeyResource)
              .build();
      return addSignedUrlKeyBackendBucket(request);
    }