[k8s] Show which Kubernetes context/cluster is used in sky status

[romilbhardwaj]

From user:

Can sky status show which k8s account is running a certain cluster? right now it's like this where the k8s ones are from 3 different clusters and it's pretty difficult to associate

Perhaps we can use the identity ({cluster}_{user}_{namespace}) as the region to show when running sky status -a?

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