refactor: Makefile, update docs

- split Makefile
  1. tools: include install tools, check tools, download dependency(gcc
     etc) and tokenizer. these will be download into "bin" folder than
     global path
  2. cluster: include k8s and ocp
  3. kind
- rename "openshift-base" to "kubernetes-base" to be clear for purpose
- uplift Go lint version to 2.1.6 to align with the same one set in
  Github Action
- rename make targets for better visibility, deprcating old ones
- add more print in "make env"

Signed-off-by: Wen Zhou <wenzhou@redhat.com>

Author: zdtsw

DEVELOPMENT.md

@@ -140,7 +140,7 @@ Operators, etc.) to support the namespace-level development environments:
 Install Gateway API + GIE CRDs:
 
 ```bash
-kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.3.0/standard-install.yaml
+kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.4.0/standard-install.yaml
 kubectl apply -f https://github.com/kubernetes-sigs/gateway-api-inference-extension/releases/latest/download/manifests.yaml
 ```
 
@@ -229,13 +229,16 @@ curl -s -w '\n' http://localhost:8080/v1/completions -H 'Content-Type: applicati
 
 **1. Setting the EPP image and tag:**
 
-You can optionally set a custom EPP image (otherwise, the default will be used):
+You can optionally set a custom EPP image and tag (otherwise, defaults will be used):
 
 ```bash
+export IMAGE_REGISTRY="<YOUR_REGISTRY>"
 export EPP_TAG="<YOUR_TAG>"
-export EPP_IMAGE="<YOUR_REGISTRY>/<YOUR_IMAGE>"
 ```
 
+> [!NOTE]
+> The full image reference will be constructed as `${EPP_IMAGE}:${EPP_TAG}`, where `EPP_IMAGE` defaults to `${IMAGE_REGISTRY}/llm-d-inference-scheduler`. For example, with `IMAGE_REGISTRY=quay.io/<my-id>` and `EPP_TAG=v1.0.0`, the final image will be `quay.io/<my-id>/llm-d-inference-scheduler:v1.0.0`.
+
 **2. Setting the vLLM replicas:**
 
 You can optionally set the vllm replicas: