refactor(scrub): replace umoci logic in scrub implementation (#1845)

- implement scrub also for S3 storage by replacing umoci
- change scrub implementation for ImageIndex
- take the `Subject` into consideration when running scrub
- remove test code relying on the umoci library. Since we started
relying on images in test/data, and we create our own images using
go code we can obtain digests by other means. (cherry picked from commit 489d4e2d23c1b4e48799283f8281024bbef6123f)

Signed-off-by: Andrei Aaron <aaaron@luxoft.com>
Signed-off-by: Andreea-Lupu <andreealupu1470@yahoo.com>

pkg/extensions/scrub/scrub.go

@@ -39,6 +39,7 @@ func RunScrubRepo(ctx context.Context, imgStore storageTypes.ImageStore, repo st
 				Str("image", result.ImageName).
 				Str("tag", result.Tag).
 				Str("status", result.Status).
+				Str("affected blob", result.AffectedBlob).
 				Str("error", result.Error).
 				Msg("scrub: blobs/manifest affected")
 		}