Add common k8s secret include

Author: mjang

content/includes/nginx-one/how-to/k8s-secret-dp-key.md

@@ -0,0 +1,23 @@
+---
+nd-docs: "DOCS-000"
+files:
+- content/nginx-one/k8s/add-ngf-manifests.md
+- content/nginx-one/k8s/add-ngf-helm.md
+---
+
+To create a Kubernetes secret, you'll need:
+
+- The Data Plane Key
+- To set up the secret in the same namespace as NGINX Gateway Fabric
+- Use the name `dataplane.key` as shown
+- A namespace. The default NGINX Gateway Fabric namespace is `nginx-gateway`
+  - You can create it with the following command: `kubectl create namespace nginx-gateway`
+
+Once you have that information, run the following command:
+
+
+   ```shell
+   kubectl create secret generic dataplane-key \
+     --from-literal=dataplane.key=<Your Dataplane Key> \
+     -n <namespace>
+   ```