TST: add test for rolling max/min/mean with DatetimeIndex over different frequencies
Follow-up work on #29761 - parametrize over different operations and frequencies

- [x] xref #21096
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Thanks @ganevgv !