Add kube_namespace tag to object count metrics

[ahmed-mez]

What does this PR do?

<object>.count metrics do not use the default kube_labels_mapper as opposed to the other metrics, it's why the kube_namespace tag was missing. This PR fixes this.

Motivation

Bug fix.

Additional Notes

The label mapper override is inspired by what we do in the ksm core check https://github.com/DataDog/datadog-agent/blob/main/pkg/collector/corechecks/cluster/ksm/kubernetes_state.go#L717-L729

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #11734 (4dad638) into master (129ddb7) will decrease coverage by 0.00%.
The diff coverage is 94.73%.

Flag	Coverage Δ
kubernetes_state	89.35% <94.73%> (-0.44%)	⬇️

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