gatewayapi: recommend the "config" approach

The "config" approach is much more convenient than
to have to concatenate flags in the extraFlags field.

Signed-off-by: Maël Valais <[email protected]>

content/docs/usage/gateway.md

@@ -54,22 +54,28 @@ To install v1.5.1 Gateway API bundle (Gateway CRDs and webhook), run the followi
 kubectl apply -f "https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.0.0/standard-install.yaml"
 ```
 
-To enable the feature in cert-manager, turn on the `GatewayAPI` feature gate:
+Since cert-manager 1.15, the Gateway API support is no longer gated behind a
+feature flag, but you still need to enable the Gateway API support.
 
-- If you are using Helm:
+To enable on the Gateway API support, use the [file-based
+configuration](../configuration/configuring-components.md#configuration-file) using the
+following `config` Helm value:
 
-  ```sh
-  helm upgrade --install cert-manager jetstack/cert-manager --namespace cert-manager \
-    --set "extraArgs={--enable-gateway-api}"
-  ```
+```yaml
+config:
+  apiVersion: controller.config.cert-manager.io/v1alpha1
+  kind: ControllerConfiguration
+  enableGatewayAPI: true
+```
 
-- If you are using the raw cert-manager manifests, add the following flag to the
-  cert-manager controller Deployment:
+The corresponding Helm command is:
 
-  ```yaml
-  args:
-    - --enable-gateway-api
-  ```
+```sh
+helm upgrade --install cert-manager jetstack/cert-manager --namespace cert-manager \
+  --set apiVersion="controller.config.cert-manager.io/v1alpha1" \
+  --set config.kind=ControllerConfiguration" \
+  --set config.enableGatewayAPI=true
+```
 
 The Gateway API CRDs should either be installed before cert-manager starts or
 the cert-manager Deployment should be restarted after installing the Gateway API