[v4.5.0] fix (platform): add importing existing vcluster to platform through helm values (#1338) (#1368)

* Backport: Copy platform/use-platform/virtual-clusters/add-virtual-clusters.mdx to platform_versioned_docs/version-4.5.0/use-platform/virtual-clusters/add-virtual-clusters.mdx

* fix broken links

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: guowenatk <[email protected]>

Author: github-actions[bot]

platform_versioned_docs/version-4.5.0/use-platform/virtual-clusters/add-virtual-clusters.mdx

@@ -114,8 +114,14 @@ Organizations often have existing deployment pipelines using tools like Helm, Ar
 
 ### Post-deployment platform registration
 
-After deploying your vCluster using your existing tools, add it to <GlossaryTerm term="platform">the Platform</GlossaryTerm> and enable full management:
+After deploying your vCluster using your existing tools, add it to <GlossaryTerm term="platform">the Platform</GlossaryTerm> and enable full management.
 
+First, login with the platform [access key](../../api/authentication):
+```bash
+vcluster platform login [domain] --access-key=[ACCESS_KEY]
+```
+
+Then, add the virtual cluster to the platform by running:
 <InterpolatedCodeBlock
   code={`# Assuming you have already deployed a vCluster using Helm, Argo CD, or another tool
 
@@ -127,6 +133,17 @@ vcluster platform add vcluster [[VAR:VCLUSTER_NAME:vc-name]] \\
   language="bash"
 />
 
+You can also use Helm values by updating the `vcluster.yaml` to include the access key of the platform as follows and then upgrade or restart
+the virtual cluster. 
+```yaml
+external:
+  platform:
+    apiKey:
+      secretName: vcluster-platform-api-key  # Defaults to vcluster-platform-api-key if undefined
+      namespace: vcluster-namespace  # Namespace to search for the secret. If undefined, it searches the vCluster namespace. If different, vCluster needs access to the target namespace.
+```
+The platform access key can only be provided as a Kubernetes Secret. You can find more information of how to create such Secret at the [`apiKey` configuration section of vCluster.](../../../vcluster/configure/vcluster-yaml/external/platform/api-key).
+
 ### Helm wrapper for VirtualClusterInstance
 
 Create a Helm chart that deploys the VirtualClusterInstance directly, allowing the Platform to manage the vCluster from creation. This approach is ideal when you want Helm to deploy the CRD but let the Platform handle the actual vCluster.