[llvm] [CI] Upstream metrics script and container definition (PR #117461)

[Nathan Gauër via llvm-commits]

https://github.com/Keenuts approved this pull request.

LGTM! Just one minor suggestion!
For 2 other comments are things we can address later on, fine to start with this PR.

https://github.com/llvm/llvm-project/pull/117461