Adds support for per container stats in runsc based on cgroups.
1. Removed the 'cgroupfs' config flag.
2. Mounts the cgroups (/sys/fs/cgroup/<controller>) which will be shared
across all containers during root/pause container startup.
3. The container cgroups (eg:/sys/fs/cgroup/controller/<container-id>) are
mounted along with other container mounts before starting the container
process if the cgroups mount is in the spec.
Updates #172
PiperOrigin-RevId: 590752853
Jing Chen
Nayana Bidari
Andrei Vagin