[llvm] [CI] Extend metrics container to log BuildKite metrics (PR #129699)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> It looks like this now also contains changes from https://github.com/llvm/llvm-project/pull/130317? Is the plan to land that first and then rebase?

Yes, working on this I realized I needed to rework the github part first, so plan on landing the refactoring PR first, then rework this one to just add the buildkite part.

https://github.com/llvm/llvm-project/pull/129699