Update Gym to Gymnasium

[Zach-Attach]

Proposed change(s)

• Updated requirement from gym 0.21 to the latest version of gymnasium
  • version currently not specified but can be for safety
• Updated pettingzoo requirement to be compatible with latest version
  • set to 1.22.0 or greater (versions that use gymnasium)
• Replaced all gym imports to gymnasium
• Updated step and reset functions in UnityToGymWrapper and UnityParallelEnv to align with Gymnasium expectations (see https://github.com/Farama-Foundation/Gymnasium/blob/main/docs/introduction/migration_guide.md for details)
  • UnityAECEnv stays the same
• Updated tests to use gymnasium and expect new step and reset functions
• Updated documentation to no longer refer to OpenAI Gym and now refer to Farama Foundation's Gymnasium

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

There is 1 open PR and 4 issues related to this addition:

• Existing PR for this lacks many of the necessary changes: Upgraded from gym to Gymnasium #6060
• Issues:
  • Feature Request: migrate from gym to gymnasium #5884
  • Feature request: upgrade to gymnasium/update pettingzoo version #5890
  • gym -> gymnasium #5995
  • UnityToGymWrapper uninstallable in up to date Python environments due to gym dependency #6059

Types of change(s)

• Bug fix
• New feature
• Code refactor
• Breaking change
• Documentation update
• Other (please describe)

Checklist

• Added tests that prove my fix is effective or that my feature works
• Updated the changelog (if applicable)
• Updated the documentation (if applicable)
• Updated the migration guide (if applicable)

Other comments

• I do not use pettingzoo or the premade environments much myself, so there may be additional fixes that are needed.
• I was unsure if I was expected to add to the changelog or migration guide since this is not an actual release, but am happy to contribute.
• This change may result in the possibility of upgrading the maximum version other dependencies (grpcio, protobuf, numpy) as well, potentially adding support for python 3.11 or newer.

[CLAassistant]

All committers have signed the CLA.