Toolbx: Make 'toolbox list --images', etc. recognize the image
    
    The toolbox(1) command identifies Toolbx images, as opposed to any
    random OCI image, by checking whether the com.github.containers.toolbox
    label matches "true".  Otherwise, the image doesn't get displayed in
    'toolbox list --images', can't be deleted with 'toolbox rmi', etc..
    
    https://bugzilla.redhat.com/show_bug.cgi?id=2242874
    https://pagure.io/pungi-fedora/pull-request/1199
    
    Signed-off-by: Debarshi Ray <rishi@fedoraproject.org>