Added role information in GetGroups API

Currently Get Groups & Get groups on behalf of return only group names, ADR #165 proposed Role to be included from this API.

As a solution, role will be retrieved from the backend if the flag, roleRequired will be true. This is a non-mandatory flag, with default as false.

All the interfaces that are retrieving the role information, will need to have this additional parameter. For the CSPs who do not have this support, the behavior will fall back to existing implementation.

For azure, we've provided the retrieval from Gremlin.

Optional response parameter is also added in the ParentReference class, to contain this Role. Since, this is optional, there will be no change in other providers response.