Create a downtime page for scheduled maintenance and server issues

[jaw12346]

Is your feature request related to a problem? Please describe.
When ACMAS is taken offline either due to intentional maintenance or due to a server issue I would like to have a default webpage posted.

Describe the solution you'd like
When intentionally bringing down the website I would like to run a command that starts a "scheduled maintenance" page. When the server goes offline unexpectedly I would like for a "server issues" page to be posted automatically.

Describe alternatives you've considered
I'm not sure how this will work, but since nginx runs as a service it may be possible to post a webpage through the default "Welcome to NGINX" page that happens when the server is offline.

[jaw12346]

This might be a partial solution:
https://owlhowto.com/how-to-change-default-index-page-on-nginx/