[Docs] Update Wiki page about Statistics

[lfgcampos]

While looking deep into Statistics, I found that the links for Prometheus are outdated.

Prometheus simple client went through a huge refactoring and the "old" simple_client only exists until version 0.16.0.
The new version, which started under version 1.x.x has a different package, classes and all.

Migration guide is well documented on their website: https://prometheus.github.io/client_java/migration/simpleclient/

Caffeine support was introduced recently: prometheus/client_java#983

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What I want with this issue?

To simply update the Statistics page (https://github.com/ben-manes/caffeine/wiki/Statistics) with more info (if possible) but, at least, the correct new Prometheus link: https://github.com/prometheus/client_java/tree/main/prometheus-metrics-instrumentation-caffeine

Ben, maybe also adding a README to the new package/module would be nice :)

[ben-manes]

Thanks! Maybe we should link to their javadoc example?

[lfgcampos]

Yes Ben, that is simple and efficient I'd say.