Fix PPO tutorial: Add gymnasium support and Mujoco rendering compatibility in Colab

[abhitorch81]

Fixes #3392

Description

This PR updates the reinforcement_ppo.py tutorial to improve compatibility with Google Colab and future-proof it for gymnasium usage.

Key Changes:

• Added fallback logic to import gymnasium if available, otherwise fall back to gym
• Dynamically select InvertedDoublePendulum-v5 or v4 based on the gym version
• Set MUJOCO_GL=osmesa in Colab/headless environments to avoid OpenGL rendering errors from Mujoco
• Ensures compatibility with Mujoco v3.1.1 and gymnasium[mujoco]

This makes the tutorial runnable out of the box in Google Colab, with improved robustness across versions.

Checklist

• The issue that is being fixed is referred in the description (see above "Fixes [BUG] - <title> Error in downloading MuJoCo Gymnasium library #3392")
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/tutorials/3401

• 📄 Preview Python docs built from this PR

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✅ No Failures

As of commit 0eaffc6 with merge base c1cd7ab ():
💚 Looks good so far! There are no failures yet. 💚

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[abhitorch81]

Note: The linkChecker CI failure is due to broken links in unrelated RL documentation pages (404s from pytorch.org/rl/reference/...). This PR does not modify any of those links.
@jonas @dreiss

[AlannaBurke]

This looks sane from doc point of view, make sure you get approval for the content

[abhitorch81]

This looks sane from doc point of view, make sure you get approval for the content

I have added changes with the Gymnasium library as Gym was failing with Google Colab so I have put a condition @AlannaBurke

[svekars]

@vmoens