IngressRoute: add an option to disable cross-namespace routing

Co-authored-by: Jean-Baptiste Doumenjou <925513+jbdoumenjou@users.noreply.github.com>

pkg/provider/kubernetes/crd/fixtures/udp/services.yml

@@ -130,3 +130,33 @@ subsets:
     ports:
       - name: myapp-ipv6
         port: 8080
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: whoamiudp-cross-ns
+  namespace: cross-ns
+
+spec:
+  ports:
+    - name: myapp
+      port: 8000
+  selector:
+    app: traefiklabs
+    task: whoamiudp
+
+---
+kind: Endpoints
+apiVersion: v1
+metadata:
+  name: whoamiudp-cross-ns
+  namespace: cross-ns
+
+subsets:
+  - addresses:
+      - ip: 10.10.0.1
+      - ip: 10.10.0.2
+    ports:
+      - name: myapp
+        port: 8000

pkg/provider/kubernetes/crd/fixtures/udp/with_cross_namespace.yml

@@ -0,0 +1,15 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRouteUDP
+metadata:
+  name: test.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - services:
+    - name: whoamiudp-cross-ns
+      namespace: cross-ns
+      port: 8000