Add support for content in config

[jvitor83]

Closes #1947

What type of PR is this?

/kind feature

What this PR does / why we need it:

Added support to content in config element.
Unit test included.

Which issue(s) this PR fixes:

Fixes #1947

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[cdrage]

This code looks amazing! Could you please update the documentation matrix as well for compatibility?

I believe we need to add another entry there. https://github.com/kubernetes/kompose/blob/main/docs/conversion.md

Otherwise, awesome code / changes and AMAZING tests. Big thanks!

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[jvitor83]

Done as asked!
@cdrage