System to label projects on PyPI with administrative statuses/attribute

[xmunoz]

To scale up our anti-abuse moderation and help package maintainers with security response, we need to be able to, for instance, mark a release as deprecated or a project as unsupported. This means we need a generic system to add, edit, and remove administrative attributes ("flags" or "statuses") to individual projects and releases. We need support to do the architectural design to implement this. (See notes from this meeting.)