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/tcp/with_cross_namespace.yml

@@ -0,0 +1,16 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRouteTCP
+metadata:
+  name: test.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: HostSNI(`foo.com`)
+    services:
+    - name: whoamitcp-cross-ns
+      namespace: cross-ns
+      port: 8000