Introduce internal/private/ImageDestinationInternalOnly
Introduce internal/private/ImageDestinationInternalOnly

The purpose is to let a transport only implement these
methods, and provide a generic fallback for the public
methods.

Should not change behavior.

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

containers/image,containers/image