cmd/image: Image pull and export/import command does validate if the artifact is gadget image

[mqasimsarfraz]

          Good question. The same happens for the pull command

$ sudo -E ig image pull docker.io/busybox
INFO[0000] Experimental features enabled
Pulling docker.io/busybox...
Successfully pulled docker.io/library/busybox:latest@sha256:c3839dd800b9eb7603340509769c43e146a74c63dca3045a8e7dc8ee07e53966

$ sudo -E ig image list
INFO[0000] Experimental features enabled
REPOSITORY                                TAG                                      DIGEST       CREATED
docker.io/library/busybox                 latest                                   c3839dd800b9

The OCI logic doesn't check if the image being pulled / imported is actually a gadget image. (It'll require to check the layers of the image and so on). I think it's fine for now.

Originally posted by @mauriciovasquezbernal in #2779 (comment)