Create plan for keeping `forum.spinalcordmri.org` up-to-date

[joshuacwnewton]

Our forum uses the Discourse forum software operating on an Ubuntu 22.04 DigitalOcean VM.

Currently, we don't have any sort of protocol for updating:

1. The Discourse software itself, and any plugins it relies on.
2. The underlying Ubuntu installation, and any packages that are installed.

Without a protocol, I've been a bit hesitant to update these manually myself, as I don't have a good sense of which are "safe" updates, and which updates risk breaking the forum.

(Previous updates have caused forum outages, adding to my hesitancy.)