type uniqTag struct {
	revision, tag string
}

// listTags lists existing revision.
func listTags(ctx context.Context, kubeClient kubernetes.Interface, writer io.Writer) error {
	tagWebhooks, err := GetRevisionWebhooks(ctx, kubeClient)
	if err != nil {
		return fmt.Errorf("failed to retrieve revision tags: %v", err)
	}
	if len(tagWebhooks) == 0 {