Convert CLI to urfave v2

Followed the Migration Guide at https://cli.urfave.org/migrate-v1-to-v2/
The major changes not pointed out in the migration guide are:
- context.Args() no longer produces a []slice, so context.Args().Slice()
  in substitued
- All cli.Global***** are deprecated (the migration guide is somewhat
  unclear on this)

Signed-off-by: Derek Nola <derek.nola@suse.com>

Vendor in urfave cli/v2

Signed-off-by: Derek Nola <derek.nola@suse.com>

Fix NewStringSlice calls

Signed-off-by: Derek Nola <derek.nola@suse.com>

cmd/ctr/commands/info/info.go

@@ -20,7 +20,7 @@ import (
 	api "github.com/containerd/containerd/v2/api/services/introspection/v1"
 	"github.com/containerd/containerd/v2/cmd/ctr/commands"
 	ptypes "github.com/containerd/containerd/v2/protobuf/types"
-	"github.com/urfave/cli"
+	"github.com/urfave/cli/v2"
 )
 
 type Info struct {
@@ -28,7 +28,7 @@ type Info struct {
 }
 
 // Command is a cli command to output the containerd server info
-var Command = cli.Command{
+var Command = &cli.Command{
 	Name:  "info",
 	Usage: "Print the server info",
 	Action: func(context *cli.Context) error {