Currently, the InferencePool status code lives in the legacy GIE plugin, e.g. internal/kgateway/extensions2/plugins/inferenceextension/endpointpicker. This code should be moved to the agentgateway inference-extension plugin, e.g. internal/kgateway/agentgatewaysyncer/backend/inference-extension.go.

As part of this effort, the legacy GIE e2e tests should be migrated to the agentgateway e2e tests, e.g. test/kubernetes/e2e/features/inferenceextension/suite.go -> test/kubernetes/e2e/features/agentgateway/inference-extension/suite.go