✨ Improve unstructured serialisation

[inteon]

Currently, we use a custom NegotiatedSerializer for unstructured serialisation. This PR proposes to use the client-go unstructured NegotiatedSerializer instead.
This serializer does try to deserialize all json blobs to unstructured structs, making it possible to use Watch together with this deserializer (see changes to pkg/client/watch.go).

[k8s-ci-robot]

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[vincepri]

🤔 Without this, is the GVK preserved? The issue linked here is still open.

[inteon]

The watch does preserve the GVK value, I added a test to prove this fa6aa54.

[vincepri]

/ok-to-test

[vincepri]

Thanks!

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: inteon, vincepri

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