Switch cmd/ to use constructor functions. (#36962)

This is a step towards potentially splitting command groups into their
own folders to clean up `cmd/` as one folder for all cli commands.
Returning fresh command instances will also aid in adding tests as you
don't need to concern yourself with the whole command tree being one
mutable variable.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

cmd/admin_user_list.go

@@ -14,16 +14,18 @@ import (
 	"github.com/urfave/cli/v3"
 )
 
-var microcmdUserList = &cli.Command{
-	Name:   "list",
-	Usage:  "List users",
-	Action: runListUsers,
-	Flags: []cli.Flag{
-		&cli.BoolFlag{
-			Name:  "admin",
-			Usage: "List only admin users",
+func newUserListCommand() *cli.Command {
+	return &cli.Command{
+		Name:   "list",
+		Usage:  "List users",
+		Action: runListUsers,
+		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:  "admin",
+				Usage: "List only admin users",
+			},
 		},
-	},
+	}
 }
 
 func runListUsers(ctx context.Context, c *cli.Command) error {