Remove mention of Istio managed certmanager (#5092)

* Remove mention of Istio managed certmanager

* Fix lint

* Number list

* Fix indent

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

Co-Authored-By: Frank Budinsky <frankb@ca.ibm.com>

content/en/docs/tasks/observability/gateways/index.md

@@ -31,6 +31,8 @@ This option covers securing the transport layer *only*. You should also configur
 addons to require authentication when exposing them externally.
 {{< /warning >}}
 
+1. [Install cert-manager](https://docs.cert-manager.io/en/latest/getting-started/install/kubernetes.html) to manage certificates automatically.
+
 1. [Install Istio](/docs/setup) in your cluster and enable the `cert-manager` flag and configure `istio-ingressgateway` to use
 the [Secret Discovery Service](https://www.envoyproxy.io/docs/envoy/latest/configuration/security/secret#sds-configuration).
 
@@ -39,8 +41,6 @@ the [Secret Discovery Service](https://www.envoyproxy.io/docs/envoy/latest/confi
     * `--set gateways.enabled=true`
     * `--set gateways.istio-ingressgateway.enabled=true`
     * `--set gateways.istio-ingressgateway.sds.enabled=true`
-    * `--set certmanager.enabled=true`
-    * `--set certmanager.email=mailbox@donotuseexample.com`
 
     To additionally install the telemetry addons, use the following Helm installation options:
 

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

@@ -13,23 +13,23 @@ You will start with a clean Istio installation, create an example service, expos
 
 ## Before you begin
 
-[Install Istio](/docs/setup/) making sure to enable ingress [gateway](/docs/reference/config/networking/v1alpha3/gateway) with Kubernetes Ingress support, [SDS](https://www.envoyproxy.io/docs/envoy/latest/configuration/security/secret) and [cert-manager](https://docs.cert-manager.io/) optional dependency during installation. Here's an example of how to do this for the [helm template](/docs/setup/install/helm/#option-1-install-with-helm-via-helm-template) installation path:
+1. [Install Istio](/docs/setup/) making sure to enable ingress [gateway](/docs/reference/config/networking/v1alpha3/gateway) with Kubernetes Ingress support, [SDS](https://www.envoyproxy.io/docs/envoy/latest/configuration/security/secret). Here's an example of how to do this for the [helm template](/docs/setup/install/helm/#option-1-install-with-helm-via-helm-template) installation path:
 
-{{< text bash >}}
-$ helm template $HOME/istio-fetch/istio \
-  --namespace=istio-system \
-  --set gateways.istio-ingressgateway.sds.enabled=true \
-  --set global.k8sIngress.enabled=true \
-  --set global.k8sIngress.enableHttps=true \
-  --set global.k8sIngress.gatewayName=ingressgateway \
-  --set certmanager.enabled=true \
-  --set certmanager.email=mailbox@donotuseexample.com \
-  > $HOME/istio-fetch/istio.yaml
-{{< /text >}}
+    {{< text bash >}}
+    $ helm template $HOME/istio-fetch/istio \
+      --namespace=istio-system \
+      --set gateways.istio-ingressgateway.sds.enabled=true \
+      --set global.k8sIngress.enabled=true \
+      --set global.k8sIngress.enableHttps=true \
+      --set global.k8sIngress.gatewayName=ingressgateway \
+      > $HOME/istio-fetch/istio.yaml
+    {{< /text >}}
 
-{{< tip >}}
-By default `istio-ingressgateway` will be exposed as a `LoadBalancer` service type. You may want to change that by setting the `gateways.istio-ingressgateway.type` installation option to `NodePort` if this is more applicable to your Kubernetes environment.
-{{< /tip >}}
+    {{< tip >}}
+    By default `istio-ingressgateway` will be exposed as a `LoadBalancer` service type. You may want to change that by setting the `gateways.istio-ingressgateway.type` installation option to `NodePort` if this is more applicable to your Kubernetes environment.
+    {{< /tip >}}
+
+1. [Install cert-manager](https://docs.cert-manager.io/en/latest/getting-started/install/kubernetes.html) to manage certificates automatically.
 
 ## Configuring DNS name and gateway