scripts: Add sync-ostree-base-containers.sh
    
    This new script implements https://pagure.io/releng/issue/11047
    for Fedora Silverblue and Kinoite.  Fedora CoreOS already
    implements this logic in a different way (and one that is
    integrated with automated testing).  Fedora IoT has not requested
    this yet, but it would be easy to add.
    
    Signed-off-by: Colin Walters <walters@verbum.org>