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>