[Kubernetes] Metricset naming for namespace: state_namespace or namespace?

[constanca-m]

The introduction of a new metricset for the namespace resource is tracked in this issue.

When trying to add the metricset with the name namespace, following the same logic we have for pods, deployments etc, we saw that kubernetes.namespace was already being used as a string. Because of, trying to introduce the object kubernetes.namespace was no longer possible:

{\"type\":\"document_parsing_exception\",\"reason\":\"[1:2039] object mapping for [kubernetes.namespace] tried to parse field [namespace] as object, but found a concrete value\"}, dropping event!","service.name":"metricbeat","ecs.version":"1.6.0"}

The workaround found was to use this new metricset with the name state_namespace. However, this is not ideal.

This issue is a reminder that maybe we should embrace the breaking change for kubernetes.namespace:

1. We should free the kubernetes.namespace as a string field.
2. Now that the field is available, we should rename the object kubernetes.state_namespace to kubernetes.namespace.

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!