Improve control plane health indicators on cluster dashboard

Description

The control plane status popover on the cluster overview page is missing some control plane components (like etcd). Additionally, the "response rate" metric may not provide a clear and complete indication of health. 

We should review the current implementation of control plane health to ensure it has an more complete list of control plane components, and replace the "response rate" metric with a more clear and actionable indicator of health. Ideally, the final solution would make it possible for individual teams to own a "dashboard health indicator" extension for their respective component.

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