Separate and organize endpoint selector manifests

We have a bunch of yamls to install the ext-proc and a sample inferencepool and inferencemodel, I think we need to organize the manifests into three categories since not all are needed at the same time:

- manifests to setup an envoy gateway
- manifests to setup an httproute
- manifests to deploy the container + an InferencePool
- manifests to install an InferenceModel

/cc @danehans 