Use XEmbeddedResource Marker

[srueg]

Summary

Apparently using the // +kubebuilder:validation:XEmbeddedResource marker is not recognized by the current CRD generator code.

Checklist

• [ ] Keep pull requests small so they can be easily reviewed.
• [ ] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, as they show up in the changelog
• [ ] Update the documentation.
• [ ] Update tests.
• [ ] Link this PR to related issues.

[ccremer]

Thanks for checking it out though :)