nixos/tor: add tor hidden service options (#28081)

* nixos/tor: add hiddenServices option

This change allows to configure hidden services more conveniently.

* nixos/tor: fix default/example mixup

* nixos/tor: use docbook in documentation

Also use more elegant optionalString for optional strings.

* tor: seperate hidden service port by newline

* tor: better example for hidden service path

a path below /var/lib/tor is usually used for hidden services