Automatic merge from submit-queue (batch tested with PRs 44868, 44350)

build external watch event so simple encoders can encode

`kube-apiserver` clients require a specific serialization of `watch.Event` to function properly.  There is no reason to allow flexibility of serialization at this point since no client would able to understand a different encoding.

I found this which trying to use a simple, unstructured json encoder and the clients kept choking on watches because it serialized without the proper json tags.

@kubernetes/sig-api-machinery-pr-reviews