refactor(nginx): simplify PHP upstream configuration in default.conf.template

# use docker DNS resolver with limited cache value for nc update or scaling

resolver 127.0.0.11 valid=5s;

upstream php-handler {

    server ${NEXTCLOUD_ADDR};

}

server {

    listen 80;

    listen [::]:80;

        fastcgi_split_path_info ^(.+?\.php)(/.*)$;

        set $path_info $fastcgi_path_info;

        set $php_upstream "${NEXTCLOUD_ADDR}";

        try_files $fastcgi_script_name =404;

        fastcgi_param modHeadersAvailable true;         # Avoid sending the security headers twice

        fastcgi_param front_controller_active true;     # Enable pretty urls

        fastcgi_pass php-handler;

        fastcgi_pass $php_upstream;

        fastcgi_intercept_errors on;

        fastcgi_request_buffering off;