fix(helm/metrics): exclude namespace if collectionMonitoring is disabled

[sumo-drosiek]

Checklist

Until the change is released, the following configuration may be use:

metadata:
  metrics:
    config:
      merge:
        processors:
          source:
            exclude:
              k8s.namespace.name: sumologic

• Changelog updated or skip changelog label added
• Documentation updated
• Template tests added for new features
• Integration tests added or modified for major features

[swiatekm]

Why no changelog entry? Looks like a normal bug fix that should be included in the changelog.