feature: Add CEL-based mutations

[xrstf]

Feature Description

CEL expressions are the new hot solution for transforming/validating custom resources in Kubernetes and it would be nice if one could use them for mutation rules in a PublishedResource.

Proposed Solution

Add CEL as an alternative next to JSON patches and the other existing mutation options.

Alternative Solutions

No response

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Additional Context

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[xrstf]

This has to wait until kcp is on Kube 1.33 unfortunately, since the relevant packages to turn a CEL program into an object patcher are only in the 1.33 kube apiserver module.