amd-bootc: Share the additional container storage

[fabiendupont]

We need to share container image storage between rootless users, so that we don't need sudo and we don't duplicate the instructlab image. This change follows the Red Hat solution to create additional image store for rootless users.

The /usr/lib/containers/storage folder can be read by anyone and new users will inherit a default configuration via /etc/skel that configures the additional storage.

The ilab wrapper is also modified to remove the impersonation code and not use sudo anymore.

Follow-up on #766

[fabiendupont]

@rhatdan, @giuseppe

[rhatdan]

LGTM