How to enforce policies for manifests in Kubernetes?
I would be inclined to implement the Open Policy Agent as this will give you the ability to define a policy similar to this:

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sContainerLimits
metadata:
  name: container-must-have-limits
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]
  parameters:
    cpu: "200m"
    memory: "1Gi"


OPA will enforce any policy you defined via an Admission Controller, beware though it's very powerful and I have bricked clusters by not thinking through the options carefully.