Make use of docker-compose.override.yml to track changes + completely disable ipv6

https://cloud.gnous.fr/apps/deck/#/board/4/card/25
https://docs.mailcow.email/post_installation/firststeps-disable_ipv6/

.gitignore

@@ -59,7 +59,6 @@ data/web/inc/vars.local.inc.php
 data/web/inc/app_info.inc.php
 data/web/nextcloud*/
 data/web/rc*/
-docker-compose.override.yml
 mailcow.conf
 mailcow.conf_backup
 rebuild-images.sh