gh-141811: Split up init.rst into multiple pages

[ZeroIntensity]

• Issue: Doc/c-api/init.rst is way too big #141811

---

📚 Documentation preview 📚: https://cpython-previews--144844.org.readthedocs.build/en/144844/c-api/index.html

[ZeroIntensity]

I'm going to merge this without an approval as there's not really anything added here that isn't already in the docs, and this is already beginning to accumulate conflicts. If someone strongly disagrees with one of the new pages here, please tag me and send a revert.

[miss-islington-app]

Thanks @ZeroIntensity for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @ZeroIntensity, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 60f3c396fe5dc56bc3a56341e2d31fd6061bb068 3.14

[miss-islington-app]

Sorry, @ZeroIntensity, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 60f3c396fe5dc56bc3a56341e2d31fd6061bb068 3.13

[bedevere-app]

GH-145061 is a backport of this pull request to the 3.14 branch.

[ZeroIntensity]

I think it'd be better to avoid backporting this to 3.13:

1. Because of Document the entire C API #141004, there shouldn't be anything more that we need to document in init.rst, so I'm not worried about conflicts.
2. There's a very good chance that some 3.14 documentation accidentally falls into the backport, because there were a lot of changes here in 3.14.