Align kompose env interpolation with k8s

[slaskis]

What type of PR is this?

/kind bug

What this PR does / why we need it:

It aligns the kompose env interpolation with the k8s according to the docs.

Which issue(s) this PR fixes:

Fixes #1906

Special notes for your reviewer:

[linux-foundation-easycla]

• ✅login: slaskis / (be5b2ff)
• ✅login: slaskis / (be5b2ff, 489b9fe)
• ✅login: slaskis / (be5b2ff, 489b9fe, 165234e)

The committers listed above are authorized under a signed CLA.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: slaskis
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