refactor(artifact): remove oci artifact support (#1359)

* refactor(artifact): remove oci artifact support
- add header to referrers call to indicated applied artifact type filters

Signed-off-by: Laurentiu Niculae <niculae.laurentiu1@gmail.com>

* feat(gc): simplify gc logic to increase coverage

Signed-off-by: Laurentiu Niculae <niculae.laurentiu1@gmail.com>

---------

Signed-off-by: Laurentiu Niculae <niculae.laurentiu1@gmail.com>

pkg/common/common.go

@@ -17,6 +17,7 @@ import (
 	"unicode/utf8"
 
 	"github.com/opencontainers/go-digest"
+	ispec "github.com/opencontainers/image-spec/specs-go/v1"
 
 	"zotregistry.io/zot/pkg/log"
 )
@@ -274,3 +275,11 @@ func DContains(slice []digest.Digest, item digest.Digest) bool {
 
 	return false
 }
+
+func GetManifestArtifactType(manifestContent ispec.Manifest) string {
+	if manifestContent.ArtifactType != "" {
+		return manifestContent.ArtifactType
+	}
+
+	return manifestContent.Config.MediaType
+}