Add support for groupBy clauses

[MaheshAravindV]

Feature description

Currently the only way to do group by (as far as I am aware) is by writing explicit queries.

Our use case:
Find sum of a certain field when grouped by another field.

Suggested feature:
Similar to how the findBy, updateBy, deleteBy queries work, would be nice to be able to just add groupBy* or groupedBy* in order to generate SQL that groups by the given field