Adding namespace and configmappropagations finalizers for the configmappropagations

[matzew]

Fixes #2642

Proposed Changes

• adding namespaces/finalizers for ConfigMapPropagation

See the OwnerReference of it:
https://github.com/openshift/knative-eventing/blob/release-next/pkg/reconciler/namespace/resources/configmappropagation.go#L32-L35

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[matzew]

With the first commit I was still getting

{
  "level": "info",
  "ts": "2020-02-26T08:57:40.256Z",
  "logger": "controller.configmappropagation-controller.event-broadcaster",
  "caller": "record/event.go:274",
  "msg": "Event(v1.ObjectReference{Kind:\"ConfigMapPropagation\", Namespace:\"default\", Name:\"eventing\", UID:\"672948a4-29e2-4f4e-8220-a6db65c2791b\", APIVersion:\"configs.internal.knative.dev/v1alpha1\", ResourceVersion:\"90576\", FieldPath:\"\"}): type: 'Warning' reason: 'ConfigMapPropagationPropagateSingleConfigMapFailed' Failed to propagate ConfigMap config-observability: error creating ConfigMap in current namespace: configmaps \"eventing-config-observability\" is forbidden: cannot set blockOwnerDeletion if an ownerReference refers to a resource you can't set finalizers on: , <nil>",
  "commit": "3982907",
  "knative.dev/controller": "configmappropagation-controller"
}

and no confimaps got propagated to the labeled namespaces,

hence adding

      - "configmappropagations/finalizers"

[lionelvillard]

/lgtm