[llvm] [CI] Rework github workflow processing (PR #130317)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

Updated the description. realized during the weekend the method was flawed, and ended-up doing something even more basic: fetch the last 1000 workflows, and extract the metrics from those.
Added a cut-off for 8 hours old workflows, and also logging the max age oldest workflow we processed to monitor in case one day we have more then 1000 workflows in the last 2 hours.

https://github.com/llvm/llvm-project/pull/130317