Provide better error messaging when env vars are missing in production

[Martinsos]

Spin off based on this coment: #175 (comment) .

Wasp should also be checking for required env vars when deployed to production. It happens sometimes to Wasp users that they forget about an env var once they deploy a Wasp app, and then those errors manifest in weird ways, and they have hard time debugging them.
If Wasp server (or client), when deployed, detected that these vars are missing, logged about it and if needed even crashed, it would be very clear that there is an issue and what it is.

We had multiple people have trouble with this, here is one of the related Discord convos: https://discord.com/channels/686873244791210014/1241745021955473548/1247977812229357668 .

[Martinsos]

One more user hitting this here: https://discord.com/channels/686873244791210014/1245842338090319912/1246584540097417286 .

[Martinsos]

One more issue with this https://discord.com/channels/686873244791210014/1250104524014616626/1250124996576284693 , i am sending it back to triage