Feature request: groupBy similar to orderBy Expression

[KalanaPerera]

Hello, world!

Recently I got to know this amazing library and this is a lifesaver when we work with external JSON APIs (to sort, filter, etc). Since Doctrine Collections has a set of functionality like:

where
andWhere
orWhere
orderBy

What about adding groupBy functionality? is there any reason why we don't have groupBy?

Thanks