[WIP] - Fixing NGINX tests

New attempt to complete NGINX support. Please consider this is a WIP. I'm aware I've to fix doc e probably some CS
I've just added this because here https://github.com/FriendsOfSymfony/FOSHttpCache/blob/master/src/ProxyClient/Nginx.php#L43 it says that the `baseURL` is required if you want to purge relative URL.

We can remove this check but then we should modify the doc