[Metricbeat] Migrate mysql/galera_status to ReporterV2

[fearful-symmetry]

See #10774

This metricset is a bit odd. There's no tests at all, and it looks like there's a lot of copy and paste from the mysql/status metricset. In the future, maybe someone cat put in a PR to clean up the code reuse. The lack of tests is a little weirder. I'm not sure if we need a new docker container added for galera?

[ruflin]

The code change overall LGTM. Did you try to run it locally to see if it still works.

I'm sure @jsoriano can add some more details here.

[jsoriano]

@fearful-symmetry yes, galera_status is basically a copy of the status metricset and the plan would be to merge one into the other. At the moment this is barely tested and marked as experimental.

Change LGTM, but it'd be good to check in any case that it still works with Galera, try with any docker image available in the docker hub. The Percona one should be maintained (https://hub.docker.com/r/percona/percona-xtradb-cluster/ - XtraDB is the Percona rebranding for Galera).

Btw, I see that we are not printing the experimental warning in New, could you add it here? Something like:

cfgwarn.Experimental("The galera_status metricset is experimental.")

[fearful-symmetry]

@jsoriano Added the log line, and it looks like it runs fine against docker.