Add dotenv-expand support so that env vars can contain other env vars about config

[prateekkathal]

I think I'll be able to get my hands on this today itself. Will create a PR soon.

[kamilmysliwiec]

We can add this feature under a flag (when enabled). Would you like to create a PR?

[msheakoski]

I will not have much time in the next 2 weeks to work on it, but I would be glad to submit a PR when I have availability if nobody else gets to it first.

[prateekkathal]

@kamilmysliwiec I was working on this and just ran npm run test:integration and it seems all tests are failing due to some changes made in @hapi/joi (v17)

This is the line that is causing the failure.

Not sure how CircleCI tests are running fine.

[kamilmysliwiec]

@prateekkathal it looks like a Joi issue - hapijs/joi#2271 (nothing we can solve on our side)

[prateekkathal]

@kamilmysliwiec As per hapijs/joi#2266, it looks like we'll have to change the documentation and ask them to run on Node v12.

Do you think we should update the hapijs/joi version for this package because of that though?

Let me know your thoughts. I'll update my node version and make a PR for this and update the documentation on nestjs/docs.nestjs.com.

[kamilmysliwiec]

Added in 0.1.0. Thank you @prateekkathal!