FR: Support OCI reference types

[developer-guy]

Once I run crane copy, it'll (at the time of writing this) copy only the image itself, but the image may have other materials attached to it such as SBOMs, attestations, signatures, etc. cosign copy command supports that, but in crane, we do not have support for this, so, it'd be better copying these materials (if any) with the image itself optionally.

cc: @dentrax @imjasonh