https://github.com/sagemath/sage/network/dependencies?page=1 knows about some our Python dependencies -- because it happens to find the build/pkgs/*/requirements.txt files of our "pip" packages.

This is, of course, highly incomplete. To add all of SageMath's dependencies, we should use the GitHub Dependency submission API. This will also make SageMath visible in our upstream projects' GitHub front pages (in the "Used by" section.)

This will need some basic Javascript coding, using https://github.com/github/dependency-submission-toolkit in a GH Actions workflow and reading in our package metadata from build/pkgs.

Bonus points for making this workflow reusable by our upstream projects, reusing the dependency information that we have for them in build/pkgs.

Depends on:

• sage --package, sage-get-system-packages: Support PURLs pkg:pypi/DISTRO-NAME, obtain dependencies of wheels from PyPI #37500 (because the Dependency API uses PURLs)