[jmx-scraper] Upload jmx-scraper releases to Maven Central

[atoulme]

I could not find the jar releases on Maven Central. Please consider uploading there on release.

[mcmho]

jmx-scraper is here on Maven Repo. - https://mvnrepository.com/artifact/io.opentelemetry.contrib/opentelemetry-jmx-scraper

Let me update the README.md so that we can have a clear idea where it is residing.

[mcmho]

PR merged.
https://github.com/open-telemetry/opentelemetry-java-contrib/blob/main/jmx-scraper/README.md is now updated.

[atoulme]

Thanks!