DOC: Add `DataFrame.to_numpy` method
- [x] closes #57016  (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Thanks @luke396  This method seems to be not the only one missing from the current (and dev) docs, e.g. https://pandas.pydata.org/pandas-docs/version/2.1/reference/api/pandas.Index.array.html. Not sure how to check for all occurrences, because this is likely not the only additional method not working... @cbrnr Thank you for the reminder. I will make an effort to locate and include the missing documents, as you mentioned earlier @meeseeksdev backport 2.2.x