Bypassing enforce mountable secrets policy imposed by the ServiceAccount admission plugin

Users may be able to launch containers that bypass the mountable secrets policy enforced by the ServiceAccount admission plugin when using ephemeral containers. The policy ensures pods running with a service account may only reference secrets specified in the service account’s secrets field. Kubernetes clusters are only affected if the ServiceAccount admission plugin and the `kubernetes.io/enforce-mountable-secrets` annotation are used together with ephemeral containers.