code: func (service *GCSService) SetObjectMetadata(ctx context.Context, params GCSObjectParams, metadata map[string]string) error {
  	attrs := storage.ObjectAttrsToUpdate{
  		Metadata: metadata,
  	}
  	_, err := service.Client.Bucket(params.Bucket).Object(params.ID).Update(ctx, attrs)
  
  	return err
  }
docs: // SetObjectMetadata reads a GCSObjectParams and a map of metedata, returning a nil on sucess and an error otherwise