nginx/site: Add support for port in failover backend

roles/nginx/site/templates/site.conf.j2

@@ -1,7 +1,11 @@
 {% if proxy is defined and proxy is not string %}
 upstream upstream_{{ site }} {
 {% for item in proxy %}
+{%   if item | regex_search(".*:[0-9]+$") %}
+    server {{ item }};
+{%   else %}
     server {{ item }}:443;
+{%   endif %}
 {% endfor %}
 }
 {% endif %}