Why create a ServiceAccount named submarine-k8s-broker-client when deploying broker？

[zcz-1020]

When the broker is deployed, a default SA named subminer-k8s-broker-client will be created in the corresponding namespace, the source code is as follows. I don't know what the sa is for, and broker-info.subm does not use this information.

func createBrokerClusterRoleAndDefaultSA(kubeClient kubernetes.Interface, inNamespace string) error {
	// Create the a default SA for cluster access (backwards compatibility with documentation)
	err := CreateNewBrokerSA(kubeClient, submarinerBrokerClusterDefaultSA, inNamespace)
	if err != nil && !apierrors.IsAlreadyExists(err) {
		return errors.Wrap(err, "error creating the default broker service account")
	}

	// Create the broker cluster role, which will also be used by any new enrolled cluster
	_, err = CreateOrUpdateClusterBrokerRole(kubeClient, inNamespace)
	if err != nil && !apierrors.IsAlreadyExists(err) {
		return errors.Wrap(err, "error creating broker role")
	}

	// Create the role binding
	_, err = CreateNewBrokerRoleBinding(kubeClient, submarinerBrokerClusterDefaultSA, submarinerBrokerClusterRole, inNamespace)
	if err != nil && !apierrors.IsAlreadyExists(err) {
		return errors.Wrap(err, "error creating the broker rolebinding")
	}

	return nil
}

[tpantelis]

It was added by this PR. The comment mentions it's for "backwards compatibility with documentation" but not exactly sure what that's referring to. @Jaanki