Update the C-API "Sub-interpreter support" Section for PEP 684

[ericsnowcurrently]

Documentation

https://docs.python.org/3.12/c-api/init.html#sub-interpreter-support

• add an entry for Py_NewInterpreterFromConfig() and PyInterpreterConfig
• section about the consequences of a Per-interpreter GIL
• fix Py_EndInterpreter() (and Py_NewInterpreter()?) about holding GIL before/after

(See https://peps.python.org/pep-0684/ and gh-99113.)

Linked PRs

• gh-107305: Update the C-API Docs for PEP 684 #107324
• [3.12] gh-107305: Update the C-API Docs for PEP 684 (gh-107324) #107402