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/asm/opcode_string.go

@@ -0,0 +1,38 @@
+// Code generated by "stringer -output opcode_string.go -type=Class"; DO NOT EDIT.
+
+package asm
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[LdClass-0]
+	_ = x[LdXClass-1]
+	_ = x[StClass-2]
+	_ = x[StXClass-3]
+	_ = x[ALUClass-4]
+	_ = x[JumpClass-5]
+	_ = x[ALU64Class-7]
+}
+
+const (
+	_Class_name_0 = "LdClassLdXClassStClassStXClassALUClassJumpClass"
+	_Class_name_1 = "ALU64Class"
+)
+
+var (
+	_Class_index_0 = [...]uint8{0, 7, 15, 22, 30, 38, 47}
+)
+
+func (i Class) String() string {
+	switch {
+	case 0 <= i && i <= 5:
+		return _Class_name_0[_Class_index_0[i]:_Class_index_0[i+1]]
+	case i == 7:
+		return _Class_name_1
+	default:
+		return "Class(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+}