Reorganize Environment Variable instructions into per-app pages

[adepssimius]

Tech debt from #381

Create a specific table for the env vars for each application then link to it from the pages for each application.
IMO it makes the most sense to put it next to the "Setup multiple instances" link under the installation instructions, since that's probably going to be the most common use case for it.

This is mostly a placeholder to keep it visible to remind me to do it.