Fixed host forwarding for subdomain reverse proxy

Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>

roles/loadbalancer/templates/nginx.conf.j2

@@ -26,6 +26,7 @@ http {
   server {
     location / {
       proxy_pass http://k3s_servers_http;
+      proxy_set_header Host $http_host;
     }
   }
 }