Allow selectively disabling database serialization

[felixbuenemann]

There should be an option like use_postgres_serializer: false to disable postgres_ext-serializers on a case by case basis, eg. through default_serializer_options in the controller, or an option passed to render :json.

This would make it easier to work with projects where not all serializers are compatible with postgres_ext-serializers and ease migration towards full database serialization.