Add support for nginx 444 default response

The default nginx 444 response drops the inbound connection without
sending any response to the client.

backend/templates/default.conf

@@ -24,6 +24,12 @@ server {
   }
 {% endif %}
 
+{%- if value == "444" %}
+  location / {
+    return 444;
+  }
+{% endif %}
+
 {%- if value == "redirect" %}
   location / {
     return 301 {{ meta.redirect }};