api/services/instrospection: add PluginInfo

The new `PlunginInfo()` call can be used for instrospecting the details
of the runtime plugin.

```console
$ ctr plugins inspect-runtime --runtime=io.containerd.runc.v2 --runc-binary=runc
{
    "Name": "io.containerd.runc.v2",
    "Version": {
        "Version": "v2.0.0-beta.0-XX-gXXXXXXXXX.m",
        "Revision": "v2.0.0-beta.0-XX-gXXXXXXXXX.m"
    },
    "Options": {
        "binary_name": "runc"
    },
    "Features": {
        "ociVersionMin": "1.0.0",
        "ociVersionMax": "1.1.0-rc.2",
        ...,
    },
    "Annotations": null
}
```

The shim binary has to support `-info` flag, see `runtime/v2/README.md`

Replaces PR 8509 (`api/services/task: add RuntimeInfo()`)

Co-authored-by: Derek McGowan <derek@mcg.dev>
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

core/runtime/v2/example/example.go

@@ -18,9 +18,11 @@ package example
 
 import (
 	"context"
+	"io"
 	"os"
 
 	taskAPI "github.com/containerd/containerd/v2/api/runtime/task/v2"
+	apitypes "github.com/containerd/containerd/v2/api/types"
 	"github.com/containerd/containerd/v2/core/runtime/v2/shim"
 	"github.com/containerd/containerd/v2/pkg/errdefs"
 	"github.com/containerd/containerd/v2/pkg/shutdown"
@@ -73,6 +75,16 @@ func (m manager) Stop(ctx context.Context, id string) (shim.StopStatus, error) {
 	return shim.StopStatus{}, errdefs.ErrNotImplemented
 }
 
+func (m manager) Info(ctx context.Context, optionsR io.Reader) (*apitypes.RuntimeInfo, error) {
+	info := &apitypes.RuntimeInfo{
+		Name: "io.containerd.example.v1",
+		Version: &apitypes.RuntimeVersion{
+			Version: "v1.0.0",
+		},
+	}
+	return info, nil
+}
+
 func newTaskService(ctx context.Context, publisher shim.Publisher, sd shutdown.Service) (taskAPI.TaskService, error) {
 	// The shim.Publisher and shutdown.Service are usually useful for your task service,
 	// but we don't need them in the exampleTaskService.