[jmxreceiver] add support for running custom Apache Groovy script at runtime

[choucavalier]

Description

Target systems are predefined Groovy scripts that define JMX Mbeans metrics that should be collected. However, they are limited in the metrics they provide.

This patch allows using a custom Groovy script at runtime when running the jmxreceiver.

Testing

I've updated the tests to include this new config. Tests are passing locally.

Documentation

I've updated the README to reflect these changes.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: choucavalier / name: Valentin Iovene (d36fe69, fb4e881)

[atoulme]

Please open an issue for discussion. The collector is trying to avoid allowing to run scripts that are too open ended and can be taken advantage of.

[breedx-splk]

I would like to respectfully caution against this. Please see #34825 and be aware that the jmx-metrics-gatherer is being deprecated in favor of the new jmx-scraper which will drop groovy in favor of yaml.

We (java side of things) are not interested in maintaining groovy scripts going forward, and the ability to execute arbitrary groovy code has always been a security liability. The current plan is to remove the jmx-metrics module once jmx-scraper is deemed good enough for production.

[hughesjj]

For more background as to why arbitrary scripts aren't permitted as part of the -contrib collector's jmx recevier, please see

• Support custom Groovy script to scrape metrics
• Review jmxreceiver from a security perspective