=per #15064 persistence perf spec is now MetricsKit enabled

* `PerformanceSpec` in akka persistence will now report metrics when run on jenkins.
* Small updates in MetricsKit (better console printing - metrics come after the test name, not before it = thanks to using info instead of println)

Useful to have before tackling https://github.com/akka/akka/issues/15227 in order to see a perf diff after the changes needed for that (though I'd suggest a specific JMH bench for eventsourced processor - will come soon).

Refs #15064