According to https://github.com/openshift/multiarch-tuning-operator/blob/main/docs/enhancements/MTO-0002-local-pod-placement.md#changes-to-the-multiarch-tuning-operator, the validating webhook for the ClusterPodPlacementConfig should deny the deletion of the singleton ClusterPodPlacementConfig unless all the PodPlacementConfigs are deleted first.

Acceptance criteria:

• The deletion of ClusterPodPlacementConfig is denied if any PodPlacementConfig is stored in the cluster's db
• Unit tests are created for each new function that has no dependencies on external services
• Integration tests might be skipped here as they might be unable to test the validating webhook behavior (double check first)
• E2E tests are implemented