docs(clientlibs): Add Prometheus kotlin client library

[Rxfa]

I'd like to add a Kotlin client I wrote a while ago.
Thanks!

Signed-off-by: Rxfa rafa3rnrn@gmail.com

[bwplotka]

Thanks 👋🏽 and great job for writing a new SDK! 💪🏽 It looks solid.

We don't have a policy on the adoption/quality bar for community exporters yet (to include them into our website), but I noticed your library does not have any release (0.0.0?) and I don't see any evidences of production users. Do you know who uses it?

[Rxfa]

Thanks for the feedback!

You're right: at the moment, we don't have know production users. The project is still at v0.0.0 because we wanted to finalize a few documentation and naming details before cutting an official release, not because of missing functionality. The SDK itself is fully implemented, tested, and already usable.

Our goal in listing it early is to make it visible so potential users can discover it, try it out, and provide feedback. We're happy to cut a v0.1.0 release and clearly state its maturity level if that helps align with the website's quality bar.

cc @mariorj16