InferencePool: Add Approval CRD Annotation

[danehans]

Once #1173 is approved (not merged), 1) update // +kubebuilder:metadata:annotations="api-approved.kubernetes.io=unapproved, experimental-only" marker to reference https://github.com/kubernetes-sigs/gateway-api-inference-extension/pull/1173.

cc: @robscott

[capri-xiyue]

It has been added https://github.com/kubernetes-sigs/gateway-api-inference-extension/blob/main/config/crd/bases/inference.networking.k8s.io_inferencepools.yaml#L5. I think we can close it @danehans

[kfswain]

Closing as the PR number will not change, even if more API adjustments are needed