ENH: Enable indexing with nullable Boolean
closes #31503 

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

I think from the discussion in https://github.com/pandas-dev/pandas/issues/31503 that this is something people want to allow.