Generate per-source-package index pages for tracker.debian.org

[stapelberg]

Suggested by pabs on #debian-doc

[stapelberg]

This requires a bit of refactoring. I made some progress on this, but it’s not quite done yet.

[stapelberg]

Almost done. The only missing thing now is caching, which I hope to get done this weekend.

[stapelberg]

Now implemented and deployed to manziarly. Should be live within a day or so. Test URL: https://manpages.debian.org/testing/src:btrfs-compsize/index.html

[stapelberg]

Now live.