refactor: where input on Relation

[coratgerl]

Currently, the WhereInput on the relation is as follows:

{ where: { users : { sessions : { accessToken : {equalTo: "accessToken"} } } } }

We should change the interface to support some other fields like isEmpty.

Proposed structure:

{ where: { users : { sessions : { have : { accessToken : {equalTo: "accessToken"} } } } } }

This issue requires some refactoring with complex code in GraphQL and should be well tested.