ENH: DatetimeArray/PeriodArray median
- [x] closes #33760
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

nanops.nanmedian needs to be re-worked, and there's a lot more we can do to share reduction tests.  saving for separate branches.
green-except-for-arm hmm conflict again, if you can rebase