[master] Add restrictions on Gateway APIs and services in the same namespace (#16602)

* Add restrictions on Gateway APIs and services in the same namespace

Fixed #16590

* Update content/en/docs/tasks/traffic-management/ingress/gateway-api/index.md

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Co-authored-by: shown <[email protected]>
Co-authored-by: Craig Box <[email protected]>

Author: 3 people

content/en/docs/tasks/traffic-management/ingress/gateway-api/index.md

@@ -360,6 +360,10 @@ In order to support Policy Attachment, e.g. when you're using the [`targetRef`](
 
 To link a `Gateway` to a `Service`, configure the `addresses` field to point to a **single** `Hostname`.
 
+{{< tip >}}
+Istio's controller will not configure the `Service` if it is in a different namespace to the `Gateway`.
+{{< /tip >}}
+
 {{< text yaml >}}
 apiVersion: gateway.networking.k8s.io/v1
 kind: Gateway