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

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> Overall LGTM.
> 
> Please wrap lines to 80 characters (or 88 given that's what Black prefers) given the LLVM coding standards.

done (not strict 80, but around for visibility)

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