feat: Support route fallback by default (#1381)

Author: CH3CHO

helm/core/templates/fallback-envoyfilter.yaml

@@ -0,0 +1,22 @@
+apiVersion: networking.istio.io/v1alpha3
+kind: EnvoyFilter
+metadata:
+  name: {{ include "gateway.name" . }}-global-custom-response
+  namespace: {{ .Release.Namespace }}
+  labels:
+    {{- include "gateway.labels" . | nindent 4}}
+spec:
+  configPatches:
+    - applyTo: HTTP_FILTER
+      match:
+        context: GATEWAY
+        listener:
+          filterChain:
+            filter:
+              name: envoy.filters.network.http_connection_manager
+      patch:
+        operation: INSERT_FIRST
+        value:
+          name: envoy.filters.http.custom_response
+          typed_config:
+            "@type": type.googleapis.com/envoy.extensions.filters.http.custom_response.v3.CustomResponse

helm/core/values.yaml

@@ -26,7 +26,7 @@ global:
   autoscalingv2API: true
   local: false # When deploying to a local cluster (e.g.: kind cluster), set this to true.
   kind: false # Deprecated. Please use "global.local" instead. Will be removed later.
-  enableIstioAPI: false
+  enableIstioAPI: true
   enableGatewayAPI: false
   # Deprecated
   enableHigressIstio: false