Pull-through package cache. Infrastructure repo, docs/package-cache.md.

https://packages.grey.ooo/alpine/ -> https://dl-cdn.alpinelinux.org/alpine/
https://packages.grey.ooo/codeload/ -> https://codeload.github.com/
https://packages.grey.ooo/github/ -> https://codeload.github.com/
https://packages.grey.ooo/packagist/ -> https://repo.packagist.org/
https://packages.grey.ooo/ubuntu/ -> http://archive.ubuntu.com/ubuntu/
https://packages.grey.ooo/ubuntu-ports/ -> http://ports.ubuntu.com/ubuntu-ports/
https://packages.grey.ooo/ubuntu-security/ -> http://security.ubuntu.com/ubuntu/