[BodyListener] introducing "disable_routes" proof of concept

Resolve https://github.com/FriendsOfSymfony/FOSRestBundle/issues/760

This is a proof of concept how we could avoid body listening on specific routes.
It definitely needs to be finalized, especially since `$request->attributes->get('_route')` didn't work (any hints)? For now it's just a hard coded url for demo purposes.