support cgroup2

* 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>

vendor/github.com/cilium/ebpf/doc.go

@@ -0,0 +1,17 @@
+// Package ebpf is a toolkit for working with eBPF programs.
+//
+// eBPF programs are small snippets of code which are executed directly
+// in a VM in the Linux kernel, which makes them very fast and flexible.
+// Many Linux subsystems now accept eBPF programs. This makes it possible
+// to implement highly application specific logic inside the kernel,
+// without having to modify the actual kernel itself.
+//
+// This package is designed for long-running processes which
+// want to use eBPF to implement part of their application logic. It has no
+// run-time dependencies outside of the library and the Linux kernel itself.
+// eBPF code should be compiled ahead of time using clang, and shipped with
+// your application as any other resource.
+//
+// This package doesn't include code required to attach eBPF to Linux
+// subsystems, since this varies per subsystem.
+package ebpf