Gif for gymnasium env

[JulienT01]

Description

Allow the save as Gif for gymnasium env (make_gym) : #453

Checklist

• My code follows the style guideline
  To check :
  black --check examples rlberry *py
  flake8 --select F401,F405,D410,D411,D412 --exclude=rlberry/check_packages.py --per-file-ignores="init.py:F401",
• I have commented my code, particularly in hard-to-understand areas,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works,
• New and existing unit tests pass locally with my changes,
• If updated the changelog if necessary,
• I have set the label "ready for review" and the checks are all green.

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[github-actions]

Hello,
The build of the doc succeeded. The documentation preview is available here:
https://rlberry-py.github.io/rlberry/preview_pr

[github-actions]

Hello,
The build of the doc succeeded. The documentation preview is available here:
https://rlberry-py.github.io/rlberry/preview_pr

[github-actions]

Hello,
The build of the doc succeeded. The documentation preview is available here:
https://rlberry-py.github.io/rlberry/preview_pr

[github-actions]

Hello,
The build of the doc succeeded. The documentation preview is available here:
https://rlberry-py.github.io/rlberry/preview_pr