Support env variables in values from envFrom

[lesaux]

What would you like to be added?

Currently if I define environment variables on container in the following way:

env:
  - name: SOME_VAR
     value: SOME_VALUE
  - name: SOME_OTHER_VAR
     value: SOME_OTHER_VALUE-$(SOME_VALUE)
envFrom:
  - secretRef:
      name: some-secret

When one of the values in the secret being set to $(SOME_VAR), that value doesn't get replaced.

SOME_OTHER_VAR gets replaced properly, but the envFrom, wether its a configmap or secret doesn't get replaced.

Why is this needed?

It would be quite nice to simplify very long manifests by removing most env: stanzas in favor of envFrom:

[k8s-ci-robot]

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[HirazawaUi]

/sig node