Support CRI v1 API

[ktock]

Fixes: #1007 #1006 #1005

This commit adds support for CRI v1 API for CRI proxy. We still support CRI v1alpha API because containerd supports it. We'll drop that API once containerd drops that API.

[ktock]

https://github.com/containerd/stargz-snapshotter/actions/runs/3572035809/jobs/6004477580#step:7:1443

github.com/k3s-io/k3s/pkg/containerd imports
	github.com/containerd/stargz-snapshotter/service/plugin imports
	github.com/containerd/containerd/third_party/k8s.io/cri-api/pkg/apis/runtime/v1alpha2: module github.com/containerd/containerd@latest found (v1.6.10, replaced by github.com/k3s-io/[email protected]), but does not contain package 

It seems that we need to maintain or own CRI API fork.

[ktock]

Added github.com/containerd/stargz-snapshotter/third_party/k8s.io/cri-api/pkg/apis/runtime/v1alpha2 as a fork of CRI API.

[ktock]

Here we introduce github.com/containerd/stargz-snapshotter/service/pluginforked.

Both of github.com/containerd/stargz-snapshotter/service/pluginforked and the current github.com/containerd/stargz-snapshotter/service/plugin register our stargz snapshotter plugin to the containerd plugin system (e.g. used by k3s). So most of user can use github.com/containerd/stargz-snapshotter/service/plugin and ignore github.com/containerd/stargz-snapshotter/service/pluginforked.

github.com/containerd/stargz-snapshotter/service/plugin depends on containerd newer than 234bf990dca4e81e89f549448aa6b555286eaa7a which contains CRI v1alpha API fork. So if the user imports stargz-snapshotter to the tool that imports older version of containerd, the user can't build it. In this case, the user needs to use github.com/containerd/stargz-snapshotter/service/pluginforked instead. This plugin contains our forked CRI v1alpha API.

The latest k3s (953c7699b413f421a9543d45d282a1d3ce8e3598) doesn't imports the recent version of containerd so they need to use github.com/containerd/stargz-snapshotter/service/pluginforked until upgrading containerd. Our k3s integration test uses github.com/containerd/stargz-snapshotter/service/pluginforked as well.

Once the user upgrade containerd to newer than 234bf990dca4e81e89f549448aa6b555286eaa7a, the uesr can't use github.com/containerd/stargz-snapshotter/service/pluginforked and protobuf code fails with the error e.g. proto: duplicate enum registered: runtime.v1alpha2.Protocol. In this case,github.com/containerd/stargz-snapshotter/service/plugin need to be used.