KEP-4322: InventoryCluster API Rename

1.Rename the "InventoryCluster" API to something that is more intuitive, less awkward, and grammatically sound. Please review the following proposed names and select any that you find to be a suitable replacement for "InventoryCluster". The API version will stay the same: "multicluster.x-k8s.io/v1alpha1". See the thread: https://github.com/kubernetes/enhancements/pull/4323/#discussion_r1507650236 for more details.