DOC: Correct/update skipna docstrings for `any` and `all` (#23109)
Also, include examples with NA values and describe treatment of NA with `skipna == False`

- [x] closes #23109
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
