docs: Adding the Gateway inference support documentation for Nginx Ga… (llm-d#1789)

* docs: Adding the Gateway inference support documentation for Nginx Gateway Fabric

* docs: Addressing comments

* docs: Addressed new set of comments

* docs: Fixed the helm command

* docs: Fixed cleaned up command

* docs: Fixed cleaned up command

* docs: Adding released version

* docs: Fixing the YAML files for test failure

* docs: Fixing the HTTP YAML file for test failure

* docs: Addressing the review comments

Author: sindhushiv

config/manifests/gateway/nginxgatewayfabric/gateway.yaml

@@ -0,0 +1,10 @@
+apiVersion: gateway.networking.k8s.io/v1
+kind: Gateway
+metadata:
+  name: inference-gateway
+spec:
+  gatewayClassName: nginx
+  listeners:
+  - name: http
+    port: 80
+    protocol: HTTP

config/manifests/gateway/nginxgatewayfabric/httproute.yaml

@@ -0,0 +1,18 @@
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: llm-route
+  namespace: default
+spec:
+  parentRefs:
+  - name: inference-gateway
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - group: inference.networking.k8s.io
+      kind: InferencePool
+      name: vllm-llama3-8b-instruct
+