Use Control Group v2 (#1329)

* Disable real-time scheduling

It seems that Linux' cgroup v2 currenlty does not support RT scheduling.

* Remove Supervisor RT support flag

With CGroups v2 we can no longer support CPU resource allocation for
realtime scheduling.

* Bump OS Agent to 1.3.0 for CGroups v2 support

buildroot-external/rootfs-overlay/usr/sbin/hassos-supervisor

@@ -89,7 +89,6 @@ if [ -z "${SUPERVISOR_CONTAINER_ID}" ]; then
         -v ${SUPERVISOR_DATA}:/data:rw \
         -e SUPERVISOR_SHARE=${SUPERVISOR_DATA} \
         -e SUPERVISOR_NAME=hassio_supervisor \
-        -e SUPERVISOR_CPU_RT=1 \
         -e SUPERVISOR_MACHINE=${SUPERVISOR_MACHINE} \
         "${SUPERVISOR_IMAGE}:latest"