docs: new registryMirror page

Author: dkoshkin

docs/content/addons/registry-mirror.md

@@ -0,0 +1,32 @@
++++
+title = "Registry Mirror"
+icon = "fa-solid fa-eye"
++++
+
+By leveraging CAPI cluster lifecycle hooks, this handler deploys an OCI [Distribution] (Distribution) registry 
+as a mirror on the new cluster at the `AfterControlPlaneInitialized` phase.
+
+Deployment of registry mirror is opt-in via the [provider-specific cluster configuration]({{< ref ".." >}}).
+
+The hook will use the [Cluster API Add-on Provider for Helm] to deploy the registry mirror resources.
+
+## Example
+
+To enable deployment of the registry mirror on a cluster, specify the following values:
+
+```yaml
+apiVersion: cluster.x-k8s.io/v1beta1
+kind: Cluster
+metadata:
+  name: <NAME>
+spec:
+  topology:
+    variables:
+      - name: clusterConfig
+        value:
+          addons:
+            registryMirror: {}
+```
+
+[Distribution]: https://github.com/distribution/distribution
+[Cluster API Add-on Provider for Helm]: https://github.com/kubernetes-sigs/cluster-api-addon-provider-helm