[devbox.json] support env_from dotenv files

[mohsenari]

Summary

NOTE: Docs update PR will follow.
As per request from users, I added support for env_from field being able to take a path to *.env file and have those env variables available in devbox shell and run.

If a duplicate env variable is specified in both .env and in the "env" section of devbox.json, the env section from devbox.json takes priority and overwrites. This I believe is the correct behavior but I'm open to discussion.

How was it tested?

see test file at testscripts/run/envfrom.test.txt

[Lagoja]

Do .env files (and our parser) also support the following format:

export S3_BUCKET=YOURS3BUCKET
export SECRET_KEY=YOURSECRETKEYGOESHERE

[mohsenari]

Do .env files (and our parser) also support the following format:

export S3_BUCKET=YOURS3BUCKET
export SECRET_KEY=YOURSECRETKEYGOESHERE

@Lagoja not common but .env file format seems to have export in front of each line in some cases .
But because .env doesn't have an official standard (although dotenv.org claims to be the creator of dotenv), some others specifications don't support the export.
So ultimately, it's up to us if we want to add it in our parser. Currently, the parser doesn't support it.

[Lagoja]

I think I'm ok to add it later, current functionality is probably good for now

[mikeland73]

This will fail if devbox is call from any other directory that is not where the devbox.json is. I don't think it makes sense to make this relative from the working directory, it should be relative from the config file directory.

[varunpalekar]

I agree with this, my project failed due to it.

[mohsenari]

@varunpalekar thanks for reminding on the issue. I made a PR to fix this, once merged it will be available in the next version of devbox.

[JoyceBabu]

If a duplicate env variable is specified in both .env and in the "env" section of devbox.json, the env section from devbox.json takes priority and overwrites. This I believe is the correct behavior but I'm open to discussion.

There are two scenarios that need to be addressed:

1. Devbox-specific override of project-specific environment variables:
   For example, if I have a .env file containing the default environment variables for the project, the current behavior allows overriding these defaults using the env section in devbox.json.

2. Overriding devbox defaults on a per-environment basis:
   How can developers override the project defaults on their individual machines? For instance, if I have an environment variable PHP_MODULES_DIR that defaults to a path on Linux, I want to override it on my MacBook. How can I achieve this?

It would be ideal to have a way to override devbox.json itself by creating a devbox.override.json, similar to how composer.override.yaml works in Docker Compose.