simplify the envoy installation

[Jeffwan]

🚀 Feature Description and Motivation

Follow up of https://github.com/vllm-project/aibrix/pull/1738

step 1

 helm install eg oci://docker.io/envoyproxy/gateway-helm --version v1.2.8 -n envoy-gateway-system --create-namespace

step 2

    # patch the configuration to enable EnvoyPatchPolicy, this is super important!
    kubectl apply -f - <<EOF
    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: envoy-gateway-config
      namespace: envoy-gateway-system
    data:
      envoy-gateway.yaml: |
        apiVersion: gateway.envoyproxy.io/v1alpha1
        kind: EnvoyGateway
        provider:
          type: Kubernetes
        gateway:
          controllerName: gateway.envoyproxy.io/gatewayclass-controller
        extensionApis:
          enableEnvoyPatchPolicy: true
    EOF

We should make it single step once https://github.com/envoyproxy/gateway/issues/7458 is supported

Use Case

simplify the steps

Proposed Solution

No response