Audit and update package metadata

[xmunoz]

If we audit and update PyPI metadata for existing projects based on already-uploaded artifacts, we can publish information about what packages depend on each other and on certain environments, and ensure a high-quality API for many tools to reuse and build upon. The current PyPI upload API relies on the upload client extracting the metadata and supplying it with the first upload request, and that isn't a valid assumption for older upload clients. Currently, our constraint is a combination of developer time, compute resources, and privileged backend database access; funding would break this bottleneck.