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/with_cross_namespace.yml

@@ -0,0 +1,91 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRoute
+metadata:
+  name: cross-ns-route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: Host(`foo.com`) && PathPrefix(`/bar`)
+    kind: Rule
+    priority: 12
+    services:
+    - name: whoami-svc
+      namespace: cross-ns
+      port: 80
+    - name: tr-svc-wrr1
+      kind: TraefikService
+    - name: tr-svc-wrr2
+      namespace: cross-ns
+      kind: TraefikService
+    - name: tr-svc-mirror1
+      kind: TraefikService
+    - name: tr-svc-mirror2
+      namespace: cross-ns
+      kind: TraefikService
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-wrr1
+  namespace: default
+
+spec:
+  weighted:
+    services:
+      - name: whoami-svc
+        namespace: cross-ns
+        weight: 1
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-wrr2
+  namespace: cross-ns
+
+spec:
+  weighted:
+    services:
+      - name: whoami-svc
+        weight: 1
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-mirror1
+  namespace: default
+
+spec:
+  mirroring:
+    name: whoami
+    port: 80
+    mirrors:
+      - name: whoami-svc
+        namespace: cross-ns
+        percent: 20
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-mirror2
+  namespace: cross-ns
+
+spec:
+  mirroring:
+    name: whoami-svc
+    port: 80
+    mirrors:
+      - name: whoami-svc
+        namespace: cross-ns
+        percent: 20
+        port: 80