when pushing manifests, zot will validate blobs (layers + config blob) are
present in repo, currently it opens(in case of filesystem storage) or download(
in case of cloud storage) each blob.
fixed that by adding a new method ImageStore.CheckBlobPresence() on storage
to check blobs presence without checking the cache like ImageStore.CheckBlob() method does.
Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>