Headless mode fixes

[vitvakatu]

Pull Request Description

#14310 broke electron package build in bazel, because reading .env* files from app/common location is not possible due to sandboxing restrictions. This PR effectively reverts .env*-related changes from #14310, (restoring the implementation as per pre-14310 develop) and instead implements a different solution for reading env in headless mode.

As GUI’s config.ts is available in packaged ASAR archive, we can read this file at runtime and thus load build-time variables.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.
• If meaningful changes were made to logic or tests affecting Enso Cloud integration in the libraries,
  or the Snowflake database integration, a run of the Extra Tests has been scheduled.
  • If applicable, it is suggested to paste a link to a successful run of the Extra Tests.