Refactor where pod revision is stored

[SaaldjorMike]

Today, we store the pod revision as an annotation on the HumioCluster CR, but we should not store any content like this on the metadata/spec parts of the custom resource.

If we must store it on the HumioCluster object, we could move it to HumioClusterStatus somewhere. Maybe just extend NodePoolStatus to include the pod revision.

[SaaldjorMike]

Also, we should find a better solution to storing alert/action/etc ID's than the current solution that stores it as an annotation where it may conflict with whatever sync'ing the desired state into the k8s objects. No longer needed once #843 is merged. The pod revision ID is still an issue though.