Fix creation of private group chats

roles/prosody/templates/prosody.cfg.lua.j2

@@ -145,6 +145,9 @@ VirtualHost "{{ domain }}"
     key = "/etc/credentials/public/{{ domain }}/privkey.pem";
     certificate = "/etc/credentials/public/{{ domain }}/fullchain.pem";
   }
+  disco_items = {
+    { "conference.jabber.{{ domain }}", "Conference rooms for {{ domain }}" };
+  }
 
 Component "conference.jabber.{{ domain }}" "muc"
   name = "Conference rooms for {{ domain }}"