Add support for transforming objects in shared informers

[dddddai]

Fixes #2146

[yue9944882]

lets define a functional interface named TransformFunc to align w/ the upsteam, also the original go function returns an error upon failure, so i think we should declare a checked exception e.g. throws ObjectTransformException. the unit test should also cover the failure path when the checked exception is thrown.

[dddddai]

also the original go function returns an error upon failure, so i think we should declare a checked exception e.g. throws ObjectTransformException.

The exception handling references addIndexers, which returns an error in client-go while in client-java it doesn't declare an exception
https://github.com/kubernetes/kubernetes/blob/v1.23.4/staging/src/k8s.io/client-go/tools/cache/shared_informer.go#L189

java/util/src/main/java/io/kubernetes/client/informer/impl/DefaultSharedIndexInformer.java

Lines 287 to 292 in a5a7ce9

	public void addIndexers(Map<String, Function<ApiType, List<String>>> indexers) {
	if (started) {
	throw new IllegalStateException("cannot add indexers to a running informer");
	}
	indexer.addIndexers(indexers);
	}

Do you mean something like this?

public interface TransformFunc {

  /**
   * @param the original object to be transformed
   * @return the transformed object
   */
  KubernetesObject transform(KubernetesObject object) throws ObjectTransformException;
}

or keep it aligned with addIndexers?

[yue9944882]

Do you mean something like this?

yes, thats exactly what i thought, as for addIndexers, i think we can keep it, it's the legacy code and it's working.

[dddddai]

OK, fixed

[yue9944882]

@dddddai thanks! one outstanding comment otherwise lgtm

[yue9944882]

/lgtm
/approve

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