Better user information for scheduled server downtimes
Description
Currently when a scheduled server downtime due to updates / reconfiguring Gitlab server during the services are down users see a 502 errorpage or even get a connection timeout. I think it would be better for user-experience if they are informed about what is really happaning instead of making them think it is a server or connection fault.
Proposal
It would be better if right from the start of the update / reconfigure users automatically see a banner/notification. While the services are down it would be nice if users are redirected to a page explaining what is going on like "Gitlab is currently reconfigured after updates. This usually only takes up to 5 minutes. Please be patient." after the update / reconfigure is done the redirect and banner can also automaticlly removed.
gitlab-ee~2975006