RFC for dynamically imported ENV variables.

[weerd]

This pull request introduces the "Dynamically Imported Environment Variables" RFC:

Establishing a system where environment variables declared in an environment's .env file are dynamically imported both on the backend and the frontend will help simplify the use of test variables and feature flags within Phoenix.

Open Questions

• @mendelB mentioned this could still be a problem with Review apps... how do we dynamically import the env variables in there? 🤔 It is a JSON file so I wonder if there's a way to generate it that isn't a crazy amount of work...