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/client.go

@@ -23,7 +23,7 @@ import (
 	"github.com/containerd/containerd/v2/pkg/epoch"
 	"github.com/containerd/containerd/v2/pkg/namespaces"
 	"github.com/containerd/log"
-	"github.com/urfave/cli"
+	"github.com/urfave/cli/v2"
 )
 
 // AppContext returns the context for a command. Should only be called once per
@@ -34,8 +34,8 @@ import (
 func AppContext(context *cli.Context) (gocontext.Context, gocontext.CancelFunc) {
 	var (
 		ctx       = gocontext.Background()
-		timeout   = context.GlobalDuration("timeout")
-		namespace = context.GlobalString("namespace")
+		timeout   = context.Duration("timeout")
+		namespace = context.String("namespace")
 		cancel    gocontext.CancelFunc
 	)
 	ctx = namespaces.WithNamespace(ctx, namespace)
@@ -55,9 +55,9 @@ func AppContext(context *cli.Context) (gocontext.Context, gocontext.CancelFunc)
 
 // NewClient returns a new containerd client
 func NewClient(context *cli.Context, opts ...containerd.Opt) (*containerd.Client, gocontext.Context, gocontext.CancelFunc, error) {
-	timeoutOpt := containerd.WithTimeout(context.GlobalDuration("connect-timeout"))
+	timeoutOpt := containerd.WithTimeout(context.Duration("connect-timeout"))
 	opts = append(opts, timeoutOpt)
-	client, err := containerd.New(context.GlobalString("address"), opts...)
+	client, err := containerd.New(context.String("address"), opts...)
 	if err != nil {
 		return nil, nil, nil, err
 	}