Add discussion of package formats, expanding "Wheel vs Egg" discussion

[jeanas]

This a discussion that I would have found useful not long ago. I seem not to be alone.

After merging this, a redirect should be added in RTD from https://packaging.python.org/en/latest/discussions/wheel-vs-egg/ to https://packaging.python.org/en/latest/discussions/package-formats/ .

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📚 Documentation preview 📚: https://python-packaging-user-guide--1397.org.readthedocs.build/en/1397/

[jeanas]

CI had a spurious failure:

(      contribute: line   77) broken    https://weblate.org/ - HTTPSConnectionPool(host='weblate.org', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f8653733950>: Failed to establish a new connection: [Errno 101] Network is unreachable'))

Can it be retried?

[jeanas]

I have updated this PR with latest main and made some minor fixes.

Review would be appreciated.

[jeanas]

Fixed the merge conflict.

Review would still be appreciated 🙂

[sinoroc]

Looks good to me.

Some comments/nitpicks, but they should not block getting this merged

[chrysle]

Thank you!