func MultiWriteToFile(p string, tagToImage map[name.Tag]v1.Image) error {
	w, err := os.Create(p)
	if err != nil {
		return err
	}
	defer w.Close()
	return MultiWrite(tagToImage, w)
}
MultiWriteToFile writes in the compressed format to a tarball, on disk.
This is just syntactic sugar wrapping tarball.MultiWrite with a new file.
package tarball
import (
	"archive/tar"
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"github.com/google/go-containerregistry/pkg/name"
	v1 "github.com/google/go-containerregistry/pkg/v1"
)
func WriteToFile(p string, tag name.Tag, img v1.Image) error {
	w, err := os.Create(p)
	if err != nil {
		return err
	}
	defer w.Close()
	return Write(tag, img, w)
}