Add pack-objects cache design notes
Part of gitlab-com/gl-infra/scalability#955 (closed).
This MR adds some design notes about the pack-objects cache that I thought would be useful, and which made more sense when they are collected in one place. You can look at the epic gitlab-com/gl-infra&372 (closed) and read all the issues and their discussions but that does not really make the information discoverable.
Edited by Jacob Vosmaer