[Docs]: Add a section about JMX to java docs

### What needs to be changed?

follow up to #7513.

The java documentation should have a section (or page?) around JMX. This is probably still a topic a lot of people are looking for, so having a few words about it will help them to find it, e.g. when they google "jmx opentelemetry"

### Name + path of the page

opentelemetry.io/docs/languages/java/

### Additional context

_No response_