ENH: Option to return -inf/inf as lower/upper bound of quantiles, see…
Add `bounded` keyword arg to `quantile` and `qcut` functions to enable unbounded quantiles with lower/upper bounds of -inf/inf.

- [x] closes #17282
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
