Add a minimal skeleton for manifest updates to copy.go
Add a minimal skeleton for manifest updates to copy.go

This does nothing so far; it will allow attaching various reasons why a
manifest may need to be modified into the general framework.

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

masters-of-cats/image,containers/image,containers/image