Require Labels in CEL expressions

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-labels
  annotations:
    policies.kyverno.io/title: Require Labels in CEL expressions
    policies.kyverno.io/category: Best Practices in CEL
    policies.kyverno.io/minversion: 1.11.0
    kyverno.io/kubernetes-version: 1.26-1.27
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Pod, Label
    policies.kyverno.io/description: Define and use labels that identify semantic attributes of your application or Deployment. A common set of labels allows tools to work collaboratively, describing objects in a common manner that all tools can understand. The recommended labels describe applications in a way that can be queried. This policy validates that the label `app.kubernetes.io/name` is specified with some value.
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: check-for-labels
      match:
        any:
          - resources:
              kinds:
                - Pod
              operations:
                - CREATE
                - UPDATE
      validate:
        cel:
          expressions:
            - expression: object.metadata.?labels[?'app.kubernetes.io/name'].orValue('') != ""
              message: The label `app.kubernetes.io/name` is required.