fix (platform): add importing existing vcluster to platform through helm values

[guowenatk]

Content Description

Add documentation of importing existing vcluster to platform through helm values

Preview Link

https://deploy-preview-1338--vcluster-docs-site.netlify.app/docs/platform/next/use-platform/virtual-clusters/add-virtual-clusters#post-deployment-platform-registration

Internal Reference

Closes DOC-311

@netlify /docs

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[github-actions]

DOC-311: Add existing vcluster using Helm

[Piotr1215]

This should focus more on the command flags, show sample vcluster.yaml and in an admonition mention that api key is needed. Also the apikey url does not resolve correctly on the preview environment.

[guowenatk]

This should focus more on the command flags, show sample vcluster.yaml and in an admonition mention that api key is needed. Also the apikey url does not resolve correctly on the preview environment.

I am not sure as I think that the way of using helm values to register the vcluster is described quite thoroughly in the apikey url https://www.vcluster.com/docs/vcluster/configure/vcluster-yaml/external/platform/api-key. If the helm example is needed like this

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.
      createRBAC: true  # Defaults to true. Automatically creates the necessary RBAC roles and role bindings to locate the secret.

then maybe I should also include how to get the secret and create the roles, which is already included in the apikey url.