Documentation is misleading for installing argocd backend plugin

[goalie-lisa]

The actual documentation for the argocd backend plugin says, that you should import the argocdServiceFactory and @roadiehq/backstage-plugin-argo-cd-backend/alpha after installing the package.

--> Documentation

As I understand it, this is not true anymore since updating the plugin version to 4.2.0.

Please update the documentation.