[release-1.13] Set cluster name label for pre-existing kubeconfig#4847

k8s-infra-cherrypick-robot wants to merge 1 commit intokubernetes-sigs:release-1.13kubernetes-sigs/cluster-api-provider-azure:release-1.13from

k8s-infra-cherrypick-robot:cherry-pick-4833-to-release-1.13k8s-infra-cherrypick-robot/cluster-api-provider-azure:cherry-pick-4833-to-release-1.13Copy head branch name to clipboard