Dev Epic: https://issues.redhat.com/browse/GITOPS-949

In theory, a user could create two ArgoCD Operands in the same namespace (e.g. foo and bar). However, this is not supported by the upstream.

We should document this soft limitation, to prevent users from trying to do so.

This should probably be a note here: https://docs.openshift.com/container-platform/4.9/cicd/gitops/installing-openshift-gitops.html