[sandbox] Add sandbox shim skeleton

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

cmd/containerd-shim-runc-v2/main.go

@@ -22,6 +22,7 @@ package main
 import (
 	"context"
 
+	_ "github.com/containerd/containerd/runtime/v2/pause"
 	"github.com/containerd/containerd/runtime/v2/runc/manager"
 	_ "github.com/containerd/containerd/runtime/v2/runc/task/plugin"
 	"github.com/containerd/containerd/runtime/v2/shim"