Rename container registry and test-infra pkg

[ahg-g]

change from the old name llm-instance-gateway to the new name gateway-api-inference-extension

[ahg-g]

the test-infra directory has been renamed.

The gcr registry not yet, we need to update the cloudbuild file when renamed: https://github.com/kubernetes-sigs/gateway-api-inference-extension/blob/main/cloudbuild.yaml

[kfswain]

There is a new process that test-infra uses to update the repo, and they had to manually create our registry before. I've hounded them quite a bit over the last couple weeks, so letting this rest till the new year, hopefully we can just use the automated process to create the new registry.

[ahg-g]

It seems we need to open an issue in kubernetes/k8s.io repo: kubernetes/k8s.io#7636