refactor: Use ProductImage::product_version internally

[sbernauer]

Description

Follow-up of #817

This way we have a single point of responsibility, which makes it easier to plug in the recommended product version later on, while maintaining the ergonomic API from #817.

Definition of Done Checklist

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1. Changes are OpenShift compatible
2. CRD changes approved
3. Integration tests passed (for non trivial changes)

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1. Code contains useful comments
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3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

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[razvan]

lgtm