Migrate doc/bootstrap to Python

[tobiasdiez]

Migrate the shell script doc/bootstrap to Python. This improves performance and is preparation for building the docs simply by running "sphinx", see #41156.

The output should be more or less equivalent, expect for minor formatting changes and better escaping of the generated shell commands.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit 6eaa2a0; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[mantepse]

I have no idea how I could help in the reviewing process here. Any hints welcome! (I don't understand shell scripts)

The changes in package.py are purely cosmetic, with the exception of adding read_system_packages, right? (I admit that I almost dislike all of them - with the exception of replacing ' with ", which I don't care about. I find breaking the lines in this way makes the code less readable)