Checkpoint dir flag doesn't seem to work

Description

When using the experimental command docker checkpoint create the --checkpoint-dir flag is ignored. Also the printed help is different from what mentioned in the documentation, i.e. there is no mention of the flags:

"docker checkpoint create" requires exactly 2 arguments.
See 'docker checkpoint create --help'.

Usage:  docker checkpoint create [OPTIONS] CONTAINER CHECKPOINT

Create a checkpoint from a running container

Reproduce

1. Start a docker container
2. Checkpoint the container with the --checkpoint-dir flag, e.g.:
   docker checkpoint create 1f7f ch1 --checkpoint-dir=./criu (I tried several different combinations without success)
3. The dir where the checkpoint should be it's empty. Instead it's stored in /var/lib/docker/containers/1f7f.../checkpoints/ch1

No error is thrown, so the flag is accepted and parsed correctly

Expected behavior

I would expect the specified folder (criu in this case) to contain the checkpoint data

docker version

Client: Docker Engine - Community
 Version:           23.0.5
 API version:       1.42
 Go version:        go1.19.8
 Git commit:        bc4487a
 Built:             Wed Apr 26 16:21:07 2023
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          23.0.5
  API version:      1.42 (minimum version 1.12)
  Go version:       go1.19.8
  Git commit:       94d3ad6
  Built:            Wed Apr 26 16:21:07 2023
  OS/Arch:          linux/amd64
  Experimental:     true
 containerd:
  Version:          1.6.20
  GitCommit:        2806fc1057397dbaeefbea0e4e17bddfbd388f38
 runc:
  Version:          1.1.5
  GitCommit:        v1.1.5-0-gf19387a
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.10.4
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.17.3
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 1
  Running: 1
  Paused: 0
  Stopped: 0
 Images: 15
 Server Version: 23.0.5
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2806fc1057397dbaeefbea0e4e17bddfbd388f38
 runc version: v1.1.5-0-gf19387a
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.0.1-060001-generic
 Operating System: Ubuntu 22.04.2 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 12
 Total Memory: 31.27GiB
 Name: mamluk-desktop
 ID: JTKJ:DNU3:SSEW:45VW:CQLQ:MUAA:L5DR:2VMD:ZMVC:SY2Y:PYE7:ZKO3
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Experimental: true
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional Info

No response

Start by reproducing docker checkpoint create with --checkpoint-dir and compare its help output with the documented flags. Trace the docker checkpoint create command implementation and checkpoint API handling; done means the specified directory contains the checkpoint data and the command help matches the documentation.