Expose Pressure Stall Information as metrics

[dqminh]

Pressure Stall Information is exposed per cgroup in cgroupv2. It's a good way to understand contention due to lack of resources ( cpu, memory, io ). For example

# /sys/fs/cgroup/system.slice/cpu.pressure
some avg10=0.00 avg60=0.00 avg300=0.00 total=306212315
full avg10=0.00 avg60=0.00 avg300=0.00 total=246733962

It would be great to expose this data source in cadvisor as metrics.

[mrunalp]

This is something @bobbypage and I talked about adding recently. Also, adding @kolyshkin here.

[dqminh]

I added support for runc here opencontainers/runc#3358, so once that goes in we can update libcontainer in cadvisor and expose the metrics here.

[bobbypage]

That would be awesome to have support in libcontainer and use it in cAdvisor. Thanks @dqminh !