Release metrics-lib 2.3.0
We need to release metrics-lib 2.3.0 in order to update CollecTor in #25827 (moved).
From looking at metrics-lib tickets, I don't see many other tickets that are close to completion that we should wait for. (I'm looking into one other ticket now, but if that takes too long, I'll skip that.)
Suggestion: let's release metrics-lib 2.3.0 this week.