Read multiple environment files by default

[dentarg]

It would be good if overman read multiple environment files by default, so you could have one file with your non-secrets, potentially checked in to make it easier for new developers to get started, and (optionally) another file with secrets, if needed.

Seeing we currently default to loading from .env if it exists, and that it is common that you have some secrets in this file, we could treat this one as the "second" file with secrets, and that it takes precedence over the first one.

Perhaps a good simple start is just to introduce reading .default.env before reading .env?

The name could be discussed and we could potentially let the names be controlled by the .foreman file?

[dentarg]

Inspiration: https://github.com/bkeepers/dotenv?tab=readme-ov-file#customizing-rails