NETCONF-1257 has defined a PlaintextStorage API. Provide a read-only implementation of PlaintextStorage based on Kubernetes Secrets.

This should be suitably integrated for the credentials use case, but generalized to support binary keys/values – perhaps through base64-encoding.

The point here is that the plaintext would be configured for the container by K8S and a read-only of those plaintexts would be available as a PlaintextStorage instance.