ENH: Implement IntegerArray reductions
- [x] ref #33790
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I'm not sure if this is the "best" way to implement these reductions (see linked issue), but in any case I figure this is better than nothing since we can get these reductions pretty much for free. As far as I can tell FloatingArray can use the same machinery.

(I'm not able to pass on kwargs here because the masked reductions don't take them all, e.g. `axis`, and various tests break as a result.)