Disable nginx server_tokens in http context (#6873)

data/conf/nginx/templates/nginx.conf.j2

@@ -13,6 +13,7 @@ events {
 http {
     include /etc/nginx/mime.types;
     default_type  application/octet-stream;
+    server_tokens off;
 
     log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                       '$status $body_bytes_sent "$http_referer" '