Enable cgroups v2 (non hybird) on FCOS

cgroupsv2.yml

systemd:
  units:
  - name: enable-cgroups-v2.service
    enabled: true
    contents: |
      [Unit]
      Description=Enable cgroups v2 (systemd.unified_cgroup_hierarchy)
      ConditionFirstBoot=true
      After=ignition-complete.target
      Before=default.target

      [Service]
      Type=oneshot
      ExecStart=/usr/bin/rpm-ostree kargs --replace systemd.unified_cgroup_hierarchy=1 --reboot

      [Install]
      WantedBy=basic.target