* only shim v2 runc v2 ("io.containerd.runc.v2") is supported
* only PID metrics is implemented. Others should be implemented in separate PRs.
* lots of code duplication in v1 metrics and v2 metrics. Dedupe should be separate PR.
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
