Add kafka to the list of jmx checks

[masci]

What does this PR do?

When SD uses auto_conf to init JMX-fetch related checks, it verifies that the check name is listed in the list JMX_CHECKS. Kafka was missing, making impossible to use SD with JMX an the autoconf config storage.

[olivielpeau]

Just a question: adding is_jmx: yes to the init_config section of the kafka auto conf yaml should work no?

That's currently the way we detect that a regular kafka.yaml file is a jmxfetch yaml config, and I don't see a reason why this detection would stop working with auto conf.

That said, even if this detection works, I don't see any reason not to merge this PR, kafka.yaml always refers to a jmxfetch config AFAIK.

[truthbk]

I think the problem is that the template generator does indeed check if the check_name is a JMX check before generating the template, if it's not found in the list, it's skipped. So this seems consistent. It's kind of a chicken and egg problem, the template might have the is_jmx set, but until we generate the template we simply consider it that, a template, not a valid configuration. We could maybe revisit, but this makes sense for now.