kgo: document KongPluginInstallation (#8034)

Co-authored-by: Patryk Małek <[email protected]>
Co-authored-by: lena-larionova <[email protected]>

app/_data/docs_nav_kgo_1.4.x.yml

@@ -103,6 +103,8 @@ items:
             url: /guides/upgrade/data-plane/rolling/
           - text: Blue / Green Deployment
             url: /guides/upgrade/data-plane/blue-green/
+      - text: Kong Custom Plugin Distribution
+        url: guides/plugin-distribution/
   - title: Reference
     icon: /assets/images/icons/icn-magnifying-glass.svg
     items:

app/_includes/md/custom-plugin.md

@@ -0,0 +1,53 @@
+<!-- Shared between KIC and KGO plugin installation -->
+## Create a custom plugin
+
+{:.note}
+> For details about plugin development for {{site.base_gateway}}, see the [Plugin Development](/gateway/{{page.release}}/plugin-development) guide.
+
+1. Create a directory with plugin code.
+
+   {:.note}
+   > If you already have a real plugin, you can skip this step.
+
+    ```bash
+    mkdir myheader
+    echo 'local MyHeader = {}
+
+    MyHeader.PRIORITY = 1000
+    MyHeader.VERSION = "1.0.0"
+
+    function MyHeader:header_filter(conf)
+      -- do custom logic here
+      kong.response.set_header("myheader", conf.header_value)
+    end
+
+    return MyHeader
+    ' > myheader/handler.lua
+
+    echo 'return {
+      name = "myheader",
+      fields = {
+        { config = {
+            type = "record",
+            fields = {
+              { header_value = { type = "string", default = "roar", }, },
+            },
+        }, },
+      }
+    }
+    ' > myheader/schema.lua
+    ```
+
+   The directory should now look like this:
+
+    ```bash
+    tree myheader
+    ```
+
+    ```bash
+    myheader
+    ├── handler.lua
+    └── schema.lua
+
+    0 directories, 2 files
+    ```

app/_includes/md/kgo/prerequisites.md

@@ -2,7 +2,7 @@
 <details class="custom" markdown="1">
 <summary>
 <blockquote class="note">
-  <p style="cursor: pointer">Before you begin ensure that you have <u>installed the {{site.kgo_product_name}}</u> in your Kubernetes cluster {% if include.aiGateway %}with AI Gateway support enabled{% endif %}. {% if include.enterprise %}This guide requires an enterprise license.{% endif %}</p>
+  <p style="cursor: pointer">Before you begin, ensure that you have <u>installed the {{site.kgo_product_name}}</u> in your Kubernetes cluster{% if include.aiGateway %} with AI Gateway support enabled{% endif %}{% if include.kongplugininstallation %} with KongPluginInstallation support enabled{% endif %}. {% if include.enterprise %}This guide requires an enterprise license.{% endif %}</p>
 </blockquote>
 </summary>
 
@@ -47,6 +47,17 @@ kubectl set env -n kong-system deployments/kgo-gateway-operator-controller-manag
 ```
 {% endif %}
 
+{%- if include.kongplugininstallation %}
+
+### Enable the KongPluginInstallation controller
+
+As this guide uses the experimental KongPluginInstallation feature, we need to explicitly enable it:
+
+```bash
+kubectl set env -n kong-system deployments/kgo-gateway-operator-controller-manager -c manager GATEWAY_OPERATOR_ENABLE_CONTROLLER_KONGPLUGININSTALLATION="true"
+```
+{% endif %}
+
 {% if include.enterprise %}
 
 ### Enterprise License