Support jsr77 j2ee statistics

[amarziali]

This PR allows fetching JSR-77 JEE Management statistic mbeans used in many application servers (jboss, weblogic, ...) to represent resources like ThreadPools.

[mcculls]

I suspect this won't work as intended in terms of unloading, because the values in the map contain class references from the class-loader, and those will stop the class-loader from being unloaded. We could wrap the values in a SoftReference to avoid pinning the class-loader while allowing the value to carry over across GC cycles.

[amarziali]

Wrapped around a softreference. Thank you for the suggestion. I completely missed this

[mcculls]

Some minor suggestions - otherwise this looks good

[carlosroman]

Tested a local build of your branch @amarziali and all working fine:

=========
JMX Fetch
=========

  Information
  ==================
    runtime_version : 11.0.22
    version : 0.49.3-SNAPSHOT
  Initialized checks
  ==================
    kafka
    - instance_name: kafka-kafka-v2-9999
      metric_count: 68
      service_check_count: 0
      message: <no value>
      status: OK
  Failed checks
  =============
    no checks