Relax the requirements of `reference.ExtractValueFn`

[muvaf]

What problem are you facing?

Because reference.ExtractValueFn requires resource.Managed interface, until the functions of the CRD types that implement that interface are generated we get compile errors, hence we can't generate those functions because angryjet requires no compile errors before starting to do any code generation.

The workaround I used in provider-jet-aws was to wrap it: https://github.com/crossplane-contrib/provider-jet-aws/blob/ee98973/apis/kms/v1alpha1/extractor.go#L11

How could Crossplane help solve your problem?

If we accept metav1.Object instead of resource.Managed, then we wouldn't have this problem since the code generator of functions that satisfy metav1.Object do not require the code to be able to compile. Another fix could be to make angryjet work with packages that have compile errors though I'm not sure if that's possible.

cc @negz @hasheddan

[muvaf]

This could also have the nice side effect of allowing referencer to work with non-Crossplane cluster-scoped resources as well, like ClusterRole or ClusterIssuer of cert-manager.

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