Useful if we wanted to create a Geo-based archive consisting of machines
in the archive_mirrors group (though this will likely not happen because
it'd break archlinux-repro due to the ~4 hour sync delay).
Ansible side of commit 5007c1a85e ("tf-stage1: allow setting the NS
TTL of geo domains"); both values need to match so our geo nameservers
report the same TTL as that returned by the parent zone's nameservers.
