pass `manifest.Digest` to `storage.store.SetImageBigData`
pass `manifest.Digest` to `storage.store.SetImageBigData`

containers/storage dropped its dependency on containers/image but
requires to pass a `Digest()` function as a callback.
Pass `manifest.Digest` to make the two libraries compatible again.

Signed-off-by: Valentin Rothberg <c8d7c67387706f1534261b1aba83f5c355c00ff5@redhat.com>

containers/image,containers/image