BUG: Fixed groupby quantile for listlike q
Closes #27526

Just a WIP right now. This is under tested for 

- [ ] `groupby(sort=False)`
- [ ] non-sorted `q`
- [ ] `groupby(multiple levels)`
@WillAyd @jbrockmendel do you have time to take a look at this? will look in AM @jbrockmendel I added your alternative implementation as a TODO once the MultiIndex issue (https://github.com/pandas-dev/pandas/issues/10710) is fixed.

> Darn. Can you add a my-idea-doesnt-work case to the tests

It's covered. CI failure is just codecov. Merging in 1 hour if there aren't any objections (only CI failure is codecov).