DOC: data_columns can take bool
The ``data_columns`` argument of ``df.to_hdf`` can take ``True`` as an argument, meaning "all columns", yet the type hint is ``Optional[List[str]]``, triggering warnings in e.g. pyCharm.

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