nginx: Allow adding extra monitoring paths in a localhost.d.

puppet/zulip/manifests/app_frontend_base.pp

@@ -53,6 +53,12 @@ class zulip::app_frontend_base {
     group  => 'root',
     mode   => '0755',
   }
+  file { '/etc/nginx/zulip-include/localhost.d/':
+    ensure => directory,
+    owner  => 'root',
+    group  => 'root',
+    mode   => '0755',
+  }
 
   $loadbalancers = split(zulipconf('loadbalancer', 'ips', ''), ',')
   if $loadbalancers != [] {

puppet/zulip/templates/nginx/zulip-enterprise.template.erb

@@ -22,6 +22,7 @@ server {
     }
 
     include /etc/nginx/zulip-include/certbot;
+    include /etc/nginx/zulip-include/localhost.d/*.conf;
 }
 <% end -%>