Merge changes from upstream skeleton

[felddy]

🗣 Description

• Rename compose file and update docs.
• Fix issues flagged by new linter versions.
• Replace setup.py with pyproject.toml for modern Python packaging.
• Rename version file to match expectations of bump script.

💭 Motivation and context

Linters started to fail due to bit rot.

🧪 Testing

Local and CI.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.