Inject Env Var from Image Label

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: inject-env-var-from-image-label
  annotations:
    policies.kyverno.io/title: Inject Env Var from Image Label
    policies.kyverno.io/category: Other
    policies.kyverno.io/severity: medium
    pod-policies.kyverno.io/autogen-controllers: none
    kyverno.io/kyverno-version: 1.6.0
    policies.kyverno.io/minversion: 1.7.0
    kyverno.io/kubernetes-version: "1.23"
    policies.kyverno.io/subject: Pod
    policies.kyverno.io/description: Container images which use metadata such as the LABEL directive in a Dockerfile do not surface this information to apps running within. In some cases, running the image as a container may need access to this information. This policy injects the value of a label set in a Dockerfile named `maintainer` as an environment variable to the corresponding container in the Pod.
spec:
  rules:
    - name: add-env-maintainer
      match:
        any:
          - resources:
              kinds:
                - Pod
      preconditions:
        all:
          - key: "{{request.operation || 'BACKGROUND'}}"
            operator: NotEquals
            value: DELETE
      mutate:
        foreach:
          - list: request.object.spec.containers
            context:
              - name: maintainer
                imageRegistry:
                  reference: "{{ element.image }}"
                  jmesPath: configData.config.Labels.maintainer || ''
            preconditions:
              all:
                - key: "{{maintainer}}"
                  operator: NotEquals
                  value: ""
            patchesJson6902: |-
              - op: add
                path: "/spec/containers/{{elementIndex}}/env/-"
                value:
                  name: MAINTAINER
                  value: "{{maintainer}}"