code: func BlobDescriptorServiceFactory(factory distribution.BlobDescriptorServiceFactory) RegistryOption {
  	return func(registry *registry) error {
  		registry.blobDescriptorServiceFactory = factory
  		return nil
  	}
  }
docs: // BlobDescriptorServiceFactory returns a functional option for NewRegistry. It sets the
  // factory to create BlobDescriptorServiceFactory middleware.