This is needed in order to provide future support for client certificates
to the backend.

Also it means that haproxy is used in all cases, with or without cache, and as
a result the "cached" version of caddy is dropped.

Let haproxy setup maxconn by itself, as it's wise enough.

Also trust that it'll detect and use proper limits, instead enforcing them in
the shell with ulimit trick (ulimit -n $(ulimit -Hn)).

As empty server alias can impact the configuration, add proper test for
checking it.