imgutil should be decoupled from`filenames`

[AkihiroSuda]

lima/pkg/qemu/imgutil/imgutil.go

Lines 31 to 55 in d5601c6

	func CreateDataDisk(dir, format string, size int) error {
	dataDisk := filepath.Join(dir, filenames.DataDisk)
	if _, err := os.Stat(dataDisk); err == nil || !errors.Is(err, fs.ErrNotExist) {
	// datadisk already exists
	return err
	}
	args := []string{"create", "-f", format, dataDisk, strconv.Itoa(size)}
	cmd := exec.Command("qemu-img", args...)
	if out, err := cmd.CombinedOutput(); err != nil {
	return fmt.Errorf("failed to run %v: %q: %w", cmd.Args, string(out), err)
	}
	return nil
	}
	func ResizeDataDisk(dir, format string, size int) error {
	dataDisk := filepath.Join(dir, filenames.DataDisk)
	args := []string{"resize", "-f", format, dataDisk, strconv.Itoa(size)}
	cmd := exec.Command("qemu-img", args...)
	if out, err := cmd.CombinedOutput(); err != nil {
	return fmt.Errorf("failed to run %v: %q: %w", cmd.Args, string(out), err)
	}
	return nil
	}

https://github.com/lima-vm/lima/blob/master/pkg/nativeimgutil/nativeimgutil.go#L38-L53

imgutils should be unaware of the internal filenames structure