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/leases/leases.go

@@ -26,11 +26,11 @@ import (
 
 	"github.com/containerd/containerd/v2/cmd/ctr/commands"
 	"github.com/containerd/containerd/v2/core/leases"
-	"github.com/urfave/cli"
+	"github.com/urfave/cli/v2"
 )
 
 // Command is the cli command for managing content
-var Command = cli.Command{
+var Command = &cli.Command{
 	Name:  "leases",
 	Usage: "Manage leases",
 	Subcommands: cli.Commands{
@@ -40,7 +40,7 @@ var Command = cli.Command{
 	},
 }
 
-var listCommand = cli.Command{
+var listCommand = &cli.Command{
 
 	Name:        "list",
 	Aliases:     []string{"ls"},
@@ -48,14 +48,15 @@ var listCommand = cli.Command{
 	ArgsUsage:   "[flags] <filter>",
 	Description: "list active leases by containerd",
 	Flags: []cli.Flag{
-		cli.BoolFlag{
-			Name:  "quiet, q",
-			Usage: "Print only the blob digest",
+		&cli.BoolFlag{
+			Name:    "quiet",
+			Aliases: []string{"q"},
+			Usage:   "Print only the blob digest",
 		},
 	},
 	Action: func(context *cli.Context) error {
 		var (
-			filters = context.Args()
+			filters = context.Args().Slice()
 			quiet   = context.Bool("quiet")
 		)
 		client, ctx, cancel, err := commands.NewClient(context)
@@ -99,24 +100,25 @@ var listCommand = cli.Command{
 	},
 }
 
-var createCommand = cli.Command{
+var createCommand = &cli.Command{
 	Name:        "create",
 	Usage:       "Create lease",
 	ArgsUsage:   "[flags] <label>=<value> ...",
 	Description: "create a new lease",
 	Flags: []cli.Flag{
-		cli.StringFlag{
+		&cli.StringFlag{
 			Name:  "id",
 			Usage: "Set the id for the lease, will be generated by default",
 		},
-		cli.DurationFlag{
-			Name:  "expires, x",
-			Usage: "Expiration of lease (0 value will not expire)",
-			Value: 24 * time.Hour,
+		&cli.DurationFlag{
+			Name:    "expires",
+			Aliases: []string{"x"},
+			Usage:   "Expiration of lease (0 value will not expire)",
+			Value:   24 * time.Hour,
 		},
 	},
 	Action: func(context *cli.Context) error {
-		var labelstr = context.Args()
+		var labelstr = context.Args().Slice()
 		client, ctx, cancel, err := commands.NewClient(context)
 		if err != nil {
 			return err
@@ -152,20 +154,20 @@ var createCommand = cli.Command{
 	},
 }
 
-var deleteCommand = cli.Command{
+var deleteCommand = &cli.Command{
 	Name:        "delete",
 	Aliases:     []string{"del", "remove", "rm"},
 	Usage:       "Delete a lease",
 	ArgsUsage:   "[flags] <lease id> ...",
 	Description: "delete a lease",
 	Flags: []cli.Flag{
-		cli.BoolFlag{
+		&cli.BoolFlag{
 			Name:  "sync",
 			Usage: "Synchronously remove leases and all unreferenced resources",
 		},
 	},
 	Action: func(context *cli.Context) error {
-		var lids = context.Args()
+		var lids = context.Args().Slice()
 		if len(lids) == 0 {
 			return cli.ShowSubcommandHelp(context)
 		}