docker_image_dest: Add OCI manifests to manifestMIMETypes

Since OCI support is in progress for the docker registry, if we have
an OCI manifest, we should try uploading it literally to the registry
before falling back to converting it to a v2 manifest.

docker/docker_image_dest.go

@@ -20,6 +20,7 @@ import (
 	"github.com/docker/distribution/registry/api/v2"
 	"github.com/docker/distribution/registry/client"
 	"github.com/opencontainers/go-digest"
+	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -56,7 +57,7 @@ func (d *dockerImageDestination) Close() error {
 
 func (d *dockerImageDestination) SupportedManifestMIMETypes() []string {
 	return []string{
-		// TODO(runcom): we'll add OCI as part of another PR here
+		imgspecv1.MediaTypeImageManifest,
 		manifest.DockerV2Schema2MediaType,
 		manifest.DockerV2Schema1SignedMediaType,
 		manifest.DockerV2Schema1MediaType,