[alerts + kube-monitoring] Common external Prometheus labels

[richardtief]

Context

Greenhouse can manage multiple clusters that might be geographically distributed. In order to uniquely identify the metrics from the clusters, to develop suitable filters in Supernova and an alert routing concept, labels must be added to the time series and alerts when communicating with external systems (federation, remote storage, Alertmanager).

Acceptance criteria

1. define a common set of labels that will be added to each time series
2. use these labels for filtering in Supernova
3. documentation to add custom concepts

[github-actions[bot]]

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