Backend protocol annotation incorrectly documented as supported for NLB

[samuel-esp]

What happened:

Inside the documentation the following statements are incorrect/unclear:

• service.beta.kubernetes.io/aws-load-balancer-backend-protocol this annoation is only supported when the underlying balancer is Classic ELB, therefore the description doesn't apply to NLB. The default protocol when this annotation is not specified is tcp not http. The description could also a bit improved a little bit to be clear to the reader

Therefore it could be usefult to further clarify the usage of the following annotation as well:

• service.beta.kubernetes.io/aws-load-balancer-type: if the annotation above is not supported for the NLB, it could not be clear how the NLB understands which protocol to use (it is automatically derived from the Kubernetes service itself). So it's better to explicitly define what is the behavior in this case

/kind bug

[k8s-ci-robot]

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