support custom group in httproute (#561)

samples/gateway-api/demo.yaml

@@ -0,0 +1,55 @@
+apiVersion: gateway.networking.k8s.io/v1alpha2
+kind: GatewayClass
+metadata:
+  name: higress-gateway
+spec:
+  controllerName: "higress.io/gateway-controller"
+---
+apiVersion: gateway.networking.k8s.io/v1alpha2
+kind: Gateway
+metadata:
+  name: higress-gateway
+  namespace: higress-system
+spec:
+  gatewayClassName: higress-gateway
+  listeners:
+  - name: default
+    hostname: "*.gateway-api.com"
+    port: 80
+    protocol: HTTP
+    allowedRoutes:
+      namespaces:
+        from: All
+---
+apiVersion: gateway.networking.k8s.io/v1alpha2
+kind: HTTPRoute
+metadata:
+  name: http
+  namespace: default
+spec:
+  parentRefs:
+  - name: higress-gateway
+    namespace: higress-system
+  hostnames: ["www.gateway-api.com"]
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    filters:
+    - type: RequestHeaderModifier
+      requestHeaderModifier:
+        add:
+        - name: my-added-header
+          value: added-value-higress
+    backendRefs:
+    - name: foo-service
+      port: 5678
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /by-nacos
+    backendRefs:
+    - name: service-provider.DEFAULT-GROUP.public.nacos
+      group: networking.higress.io
+