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>

cmd/ctr/commands/commands.go

@@ -96,6 +96,19 @@ var (
 		},
 	}
 
+	// RuntimeFlags are cli flags specifying runtime
+	RuntimeFlags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "runtime",
+			Usage: "Runtime name or absolute path to runtime binary",
+			Value: defaults.DefaultRuntime,
+		},
+		cli.StringFlag{
+			Name:  "runtime-config-path",
+			Usage: "Optional runtime config path",
+		},
+	}
+
 	// ContainerFlags are cli flags specifying container options
 	ContainerFlags = []cli.Flag{
 		cli.StringFlag{
@@ -138,19 +151,10 @@ var (
 			Name:  "read-only",
 			Usage: "Set the containers filesystem as readonly",
 		},
-		cli.StringFlag{
-			Name:  "runtime",
-			Usage: "Runtime name or absolute path to runtime binary",
-			Value: defaults.DefaultRuntime,
-		},
 		cli.StringFlag{
 			Name:  "sandbox",
 			Usage: "Create the container in the given sandbox",
 		},
-		cli.StringFlag{
-			Name:  "runtime-config-path",
-			Usage: "Optional runtime config path",
-		},
 		cli.BoolFlag{
 			Name:  "tty,t",
 			Usage: "Allocate a TTY for the container",