Add build environment to info.json

[lrandersson]

Description

This PR adds a new key to the file info.json containing a list of packages that are installed in the environment used to build the installer.
Small sample image from the file info.json that is produced when I build the test example outputs using my local conda environment:

  "_build_environment_packages": [
    {
      "name": "zstandard",
      "version": "0.24.0",
      "build": "py313h3d778a8_0",
      "build_number": 0,
      "channel": "https://repo.anaconda.com/pkgs/main/linux-64",
      "subdir": "linux-64",
    ...

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[marcoesters]

Since it's only needed for the info.json output, maybe this should move to the output section. If we don't output that file, we don't need to gather all this data.