Roles support for generic filters

[abozhilov]

Would be great if it's possible to specify certain filter/ordering fields for different roles.
e.g.

class SomeViewSet(mixins.RoleViewSetMixin, viewsets.ModelViewSet):
    """
    API endpoint that allows SomeModel to be viewed or edited.
    """
    queryset = SomeModel.objects.all()
    filter_backends = (filters.OrderingFilter, filters.SearchFilter)
    
    ordering_fields_for_group1 = ('first_name', 'middle_name', 'last_name', 'birth_date')
    ordering_fields_for_group2 = ('first_name',)
    
    search_fields_for_group1 = ('first_name', 'middle_name', 'last_name')
    search_fields_for_group2 = ('first_name',)

[r1b]

Hello,

Could add a property registry as well as a method registry - PRs welcome!