Update docs to reference versioned container images

[keithmattix]

What would you like to be added:
Docs should reference registry.k8s.io/gateway-api-inference-extension/epp (and other relevant images as necessary) instead of the k8s-staging-images path. Example: https://gateway-api-inference-extension.sigs.k8s.io/guides/serving-multiple-inference-pools-latest/?h=api+inference+extension#deploy-body-based-routing-extension.

Why this is needed:
It's important that users expecting a GA product have docs that show them where the versioned, production images can be pulled from

[youngnick]

I think this is just a holdover from before we actually had production images for things. Agreed we should be using the production images, not staging ones.