[feature] adopt cluster inventory API from k8s-sig multi-cluster

[zhiying-lin]

The community is discussing a unified Cluster Inventory API for cluster registry info.

The spec likes below:

apiVersion: multicluster.x-k8s.io/v1alpha1
kind: ClusterInventory
metadata:
 name: some-cluster
spec:
 accessObjectRefs: # optional object points to the resource that declares how to access the cluster
 - group: someGroup
   resource: someResource
   name: someName
   namespace: someNamespace
   type: KUBECONFIG
 taints:
   - key: key1
     value: value1
     effect: NoSchedule
     addTime: xxx
 healthinessProbe:
   heartbeatIntervalSeconds: 60
status:
 version:
   kubernetes: 1.26.1
 resources: # total resources of a cluster
   capacity:
     cpu: 12
     memory: 12Gi
   allocatable:
     cpu: 10
     memory: 16Gi
 properties:
   - name: clusterset.k8s.io
     value: some-clusterset
 conditions:
   - type: Healthy
     status: True
     lastTransitionTime: "2023-05-08T07:58:55Z"
     message: ""

It‘s similar to our membercluster object.

Once the community has an unified API, fleet can migrate to it and benefit from that. So that we can easily integrate with other multi-cluster projects, such as KubeVela, argoWorkflow and argoCD.