Observability for Google Kubernetes Engine: Added a dashboard for Tensor Processing Unit (TPU) metrics on the Observability tab of both the cluster listing and cluster details pages for GKE clusters

## Feature Observability for Google Kubernetes Engine: Added a dashboard for Tensor Processing Unit (TPU) metrics on the Observability tab of both the cluster listing and cluster details pages for GKE clusters. The charts on this dashboard are populated with data only if the cluster [has TPU nodes](https://cloud.google.com/kubernetes-engine/docs/concepts/tpus) and [GKE system metrics](https://cloud.google.com/kubernetes-engine/docs/how-to/configure-metrics#system-metrics) is enabled. For more information, see [View observability metrics](https://cloud.google.com/kubernetes-engine/docs/how-to/view-observability-metrics).