📝 Add StrEnum example for python 3.11+

[Matthieu-LAURENT39]

Python 3.11 added StrEnum, that can replace using MyEnum(str, Enum).

This adds that usage to the Enum parameter type docs, while also keeping the old usage for users on older versions of Python.

[github-actions]

📝 Docs preview for commit 7bd4597 at: https://af13581c.typertiangolo.pages.dev

[svlandeg]

Thanks for the contribution! I'll update this with master and add a test to double check the behaviour 🙏

[UPDATE] something seems up with the docs-building part of the CI (unrelated to this PR) - we'll look into that first.

[UPDATE 2] CI fixed 😎

[github-actions]

📝 Docs preview for commit ec692a6 at: https://ac610b93.typertiangolo.pages.dev

[github-actions]

📝 Docs preview for commit 918563e at: https://a59ac027.typertiangolo.pages.dev

[svlandeg]

Quick update: we'll pause this PR for a bit, as we want to put a mechanism in place first to have source examples for different Python versions, as well as corresponding tests that require specific Python versions too. We'll get back to this PR once we've taken care of that!