This translates all Fedora CoreOS system groups (i.e. those coming
from group manifest) into equivalent sysusers.d fragments.

We currently ship four kinds of system groups:
 * basic groups coming from the `/etc/group` file in the `setup`
   package (10-groups-basic.conf)
 * the legacy GID for the `nobody` group (00-group-nobody.conf)
 * extra groups with static GIDs that adhere to the Fedora
   allocation table (10-groups-static-extra.conf)
 * extra groups with static GIDs that are specific to CoreOS
   (00-groups-coreos-static.conf)

These sysusers.d fragments are meant as a transitory measure to
help migrate the existing group entries from the current nss-altfiles
setup to a plain sysusers.d world.