Prevent indexing of DOMjudge instance

See: DOMjudge/domjudge#2654

Author: vmcj

provision-contest/ansible/roles/domserver/templates/nginx-domjudge-inner.j2

@@ -67,6 +67,7 @@ add_header X-Frame-Options "DENY";
 add_header Referrer-Policy "same-origin";
 add_header X-Content-Type-Options "nosniff";
 add_header X-XSS-Protection "1; mode=block";
+add_header X-Robots-Tag "none" always;
 
 error_log /var/log/nginx/domjudge.log;
 access_log /var/log/nginx/domjudge.log dj_access;