[Backend] Setup environment variables for staging (dev vs prod) -- Investigation and Implementation

[bglossner]

We are going to want to switch out certain things in our app based on the environment.

For now, you can just make this change based on the port. This will change later but this is good enough for testing.

Here's an example search that may yield stuff that's useful: "node express backend environment variables prod vs dev" -- https://www.google.com/search?q=node+express+backend+environment+variables+prod+vs+dev&rlz=1C1CHBF_enUS798US798&oq=node+express+backend+environment+variables+prod+vs+dev&aqs=chrome..69i57j33i160l2j33i299.56115j0j7&sourceid=chrome&ie=UTF-8

NOTE: We do want this to be "correct" in a sense so it's worth spending the time investigating for the best solution. Please write down any findings on things that do work and don't work and pros/cons of different approaches and why we want to use the way you have suggested. It's fine if this write up is short... because React recommends it officially is totally ok for a reason.

• Investigation
• Documentation
• Implementation