Improve Metricbeat Kubernetes Volumes dashboard as currently it doesn't show useful information

[eedugon]

Describe the enhancement:

The main visualization in our [Metricbeat Kubernetes] Volumes default dashboard is not showing useful information, because the volume name is something generic and usually reused by a lot of pods. It could also mislead users.

For example this visualization is a bit meaningless as the names don't really identify much and actually belong to multiple pods:

Also, the metrics on datadir could be misleagind, as they are averages from a lot of real volumes belonging to different pods.

My proposal would be something like this, very similar, but including the pod names. As you can see the information is clearer.

I have included that visualization as part of a bigger dashboard here, in case you want to take a look.

Describe a specific use case for the enhancement or feature:

Kubernetes Monitoring with Metricbeat or Elastic Agent using the volume metricset.

cc: @gizas

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)

[gizas]

We will keep this issue open because although we have merged an update for the Volumes dashboard still the pod metadata enrichment is not possible without an enhancement (see comment)

To be tracked as part of #39524, where we will need to include the metadata pod watcher in the volume metricset and enrich relevant metrics with pod information