copy: provide compression info about copied blobs
copy: provide compression info about copied blobs

When copying a compressed blob without making any modifications to it,
set the CompressionFormat in the returned BlobInfo to reflect the
compression algorithm that was used to compress the blob.

Signed-off-by: Nalin Dahyabhai <f562fcb2a0b898bf0be1afc867ea92325d8f825f@redhat.com>

containers/image,containers/image