The validating web hook for the PodPlacementConfig should deny creation if another PodPlacementConfig in the same namespace has the same value for the priority field
According to https://github.com/openshift/multiarch-tuning-operator/blob/main/docs/enhancements/MTO-0002-local-pod-placement.md#implementation-detailsnotesconstraints

Acceptance criteria:

• The validating web hook for the PodPlacementConfig denies creation if another PodPlacementConfig in the same namespace has the same value for the priority field
• Unit tests for each new added function that does not depend on external services
• Integration tests might be skipped as the integration test suite might be unable to test the behavior of the validating webhook
• E2E tests are implemented