clusteradm proxy kubectl does not allow multiple clusters

[cwen11]

clusteradm proxy kubectl takes in a generic ClusterOption which includes both the option to specify a single cluster or multiple clusters (--clusters), but the code seems to only accept a single cluster

clusteradm/pkg/cmd/proxy/kubectl/cmd.go

Line 74 in 329f6fe

_, err = clusterClient.ManagedClusters().Get(context.TODO(), o.ClusterOption.Cluster, metav1.GetOptions{})

. This should be explicitly stated as a limitation and not appear in the --help output of the command, should be supported, or there should be a clearer error message ("resource name may not be empty").

[qiujian16]

/kind bug