[Feature] Fleet: Multi-cluster Kubernetes object visibility

Today, Fleet allows customers to put multiple Kubernetes clusters into one fleet ([link](https://learn.microsoft.com/en-us/azure/kubernetes-fleet/overview)), such that customers can gain visibility into the configurations of multiple clusters easily.


However, it doesn't provide the capability to browse Kubernetes resources or objects across multiple clusters.

This feature enables customers to list/filter native Kubernetes objects within a fleet across multiple clusters, including namespaces, pods, deployments, statefulsets, etc., similar with single cluster experience in AKS: