* Add "skip-rbac-setup" flag to "cluster add" command
"InstallClusterManagerRBAC" method of the clusterauth package
is somewhat opinionated about rolebindings and role definitions
for "argocd-manager" SA. Sometimes it is desirable however to manually
pre-configure such bindings and/or modify them in order to comply
with existing infrastructure requirements.
This commit introduces a new option "--skip-rbac-setup" which allows operator
to skip the aforementioned "InstallClusterManagerRBAC" method call.
* Modified --skip-rbac-setup into --service-account flag
* use reference instead of hardoded SA name
