kind.md cleanup deletes configmap app but create step uses kf-cm

[ytimocin]

In content/en/docs/getting-started/kind.md, the "Create sample resources" step creates:

kubectl create configmap kf-cm -n kubefleet-sample --from-literal=data=test

But the "Clean things up" section deletes:

kubectl delete configmap app -n kubefleet-sample

The cleanup command references app, which was never created in this tutorial. It should be kf-cm to match the create step.