Deployer: Evaluate Inference Extension Support

[danehans]

When #10684 merges, the Deployer will support managing k8s objects, e.g. Deployment, to run the endpoint picker inference extension. The following questions should be answered to improve supporting future extensions:

1. Should Kgateway continue to support managing the infra for inference extensions? The answer to this question may depend on the results of this upstream issue.
2. If Kgateway continues to support managing k8s objects for an inference extension, should an extension point be added to the Deployer?

[danehans]

cc: @lgadban

[danehans]

The InferencePool never added support to InferencePool for implementation-based EPP deployment, so the EPP deployer should be deprecated and removed.

[jenshu]

discussed with @danehans and we want to add deprecation messages for inference ext auto provisioning now. will take care of this along with #12372