www/bunkerweb: Enable ModSecurity when the module is available
Render the ModSecurity directives only if
ngx_http_modsecurity_module.so is installed, like upstream does for
the stream module. Build www/openresty with the MODSECURITY option to
get it.
Point the remaining paths at their FreeBSD locations, error pages,
assets and rule files were read from /usr/share/bunkerweb.
Sponsored by: Netzkommune GmbH