Introduce a BlobInfoCache interface
Introduce a BlobInfoCache interface

This will be used to record information about copied layers, and avoid the copies
if possible.

Does not add any users, so does not change behavior yet.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/image,containers/image