Add support for loading env values

[SpencerKaiser]

Pre-requisites:

• Yes, I looked through both open and closed issues looking for what I needed

Feature Description

We should support being able to store secrets in file(s) that the user can load (although the file should not be required to start the app - as in a production environment where .env is usually not present).

While supporting this, we should consider allowing multiple environments like [dotenv-flow] and we should also consider how users will import values from things like VCAP_SERVICES.

[nkahlor]

This would be super helpful to have, I'm gonna create a fork and see if I have enough time to get this working!