fix: use Docker image index and manifests

Empty image sets Docker manifest schema
and not OCI. Image manifests included in
OCI image index, and to keep consistency
all of them should have Docker media types.

Signed-off-by: Ben Oukhanov <boukhanov@redhat.com>

pkg/build/build.go

@@ -8,6 +8,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/partial"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 const (
@@ -29,12 +30,12 @@ func ContainerDiskConfig(checksum string, envVariables map[string]string) v1.Con
 }
 
 func ContainerDisk(imgPath, imgArch string, config v1.Config) (v1.Image, error) {
-	img := empty.Image
 	layer, err := tarball.LayerFromOpener(StreamLayerOpener(imgPath))
 	if err != nil {
 		return nil, fmt.Errorf("error creating an image layer from disk: %v", err)
 	}
 
+	img := mutate.MediaType(empty.Image, types.DockerManifestSchema2)
 	img, err = mutate.AppendLayers(img, layer)
 	if err != nil {
 		return nil, fmt.Errorf("error appending the image layer: %v", err)
@@ -79,5 +80,6 @@ func ContainerDiskIndex(images []v1.Image) (v1.ImageIndex, error) {
 		})
 	}
 
-	return mutate.AppendManifests(empty.Index, indexAddendum...), nil
+	idx := mutate.IndexMediaType(empty.Index, types.DockerManifestList)
+	return mutate.AppendManifests(idx, indexAddendum...), nil
 }