Hardcoded openshift-gitops operator dependency

Currently you are [hardcoded](https://github.com/validatedpatterns/patterns-operator/blob/main/controllers/subscription.go#L36) to use the openshift-gitops operator. So if user has already installed the ArgoCD, the validated patterns won't work. Would be nice to give the user option to use it's own Argo instance and specify properly configured Argo cd instance namespace.