nixos/nginx: add comment about clearing Connection header (#214211)

        proxy_send_timeout      ${cfg.proxyTimeout};

        proxy_read_timeout      ${cfg.proxyTimeout};

        proxy_http_version      1.1;

        # don't let clients close the keep-alive connection to upstream

        # don't let clients close the keep-alive connection to upstream. See the nginx blog for details:

        # https://www.nginx.com/blog/avoiding-top-10-nginx-configuration-mistakes/#no-keepalives

        proxy_set_header        "Connection" "";

        include ${recommendedProxyConfig};

      ''}