Document special case for gateway install on OpenShift (#13855)

Documents the changes here: https://github.com/istio/istio/pull/46898

content/en/docs/setup/additional-setup/gateway/index.md

@@ -106,6 +106,16 @@ To see possible supported configuration values, run `helm show values istio/gate
 The Helm repository [README](https://artifacthub.io/packages/helm/istio-official/gateway) contains additional information
 on usage.
 
+{{< tip >}}
+
+When deploying the gateway in an OpenShift cluster, use the `openshift-values.yaml` file to override the default values, for example:
+
+{{< text bash >}}
+$ helm install istio-ingressgateway istio/gateway -n istio-ingress -f @manifests/charts/gateway/openshift-values.yaml@
+{{< /text >}}
+
+{{< /tip >}}
+
 {{< /tab >}}
 
 {{< tab name="Kubernetes YAML" category-value="yaml" >}}

content/en/docs/setup/additional-setup/gateway/snips.sh

@@ -53,7 +53,11 @@ kubectl create namespace istio-ingress
 helm install istio-ingressgateway istio/gateway -n istio-ingress
 }
 
-! read -r -d '' snip_deploying_a_gateway_4 <<\ENDSNIP
+snip_deploying_a_gateway_4() {
+helm install istio-ingressgateway istio/gateway -n istio-ingress -f manifests/charts/gateway/openshift-values.yaml
+}
+
+! read -r -d '' snip_deploying_a_gateway_5 <<\ENDSNIP
 apiVersion: v1
 kind: Service
 metadata:
@@ -130,7 +134,7 @@ subjects:
   name: default
 ENDSNIP
 
-snip_deploying_a_gateway_5() {
+snip_deploying_a_gateway_6() {
 kubectl create namespace istio-ingress
 kubectl apply -f ingress.yaml
 }

content/en/docs/setup/additional-setup/gateway/test.sh

@@ -43,9 +43,9 @@ _wait_for_deployment istio-ingress istio-ingressgateway
 rebuild
 # shellcheck disable=SC2154
 cat <<EOF >ingress.yaml
-$snip_deploying_a_gateway_4
+$snip_deploying_a_gateway_5
 EOF
-snip_deploying_a_gateway_5
+snip_deploying_a_gateway_6
 _wait_for_deployment istio-ingress istio-ingressgateway
 
 istioctl install --skip-confirmation --set profile=minimal --set revision=canary