Add API-level Secret verification to the Part 12 encryption smoke test

[JNasri]

While completing the Data Encryption section in docs/12-smoke-test.md, I successfully verified that the raw value stored in etcd begins with k8s:enc:aescbc:v1:key1.

It would also be helpful to verify that the API server can retrieve and decode the encrypted-at-rest Secret correctly.

I suggest adding this command after the etcd hexdump check:

kubectl get secret kubernetes-the-hard-way -o yaml

Example output:

apiVersion: v1
data:
  mykey: bXlkYXRh
kind: Secret
metadata:
  name: kubernetes-the-hard-way
  namespace: default
type: Opaque

The output should contain mykey: bXlkYXRh, which is the value mydata encoded using Base64.

Optionally, the original value can also be verified with:

kubectl get secret kubernetes-the-hard-way \
  -o jsonpath='{.data.mykey}' | base64 --decode
echo

Expected output:

mydata