Add clusterName in GCPManagedControlPlaneSpec e2e template

Author: cpinjani

test/e2e/data/cluster-templates/gcp-gke.yaml

@@ -34,6 +34,7 @@ metadata:
   name: "${CLUSTER_NAME}-control-plane"
   namespace: "${NAMESPACE}"
 spec:
+  clusterName: "${CLUSTER_NAME}"
   project: "${GCP_PROJECT}"
   location: "${GCP_REGION}"
 ---