Upstream issue: https://github.com/argoproj-labs/argocd-image-updater/issues/1341 

1. Documentation: The requirement for --argocd-namespace flag should be clearly documented for cross-namespace deployments
2. RBAC requirements: The need for watch permissions on both secrets and configmaps should be documented
3. Configuration method: Could this be configurable via ConfigMap instead of requiring CLI args? This would make it easier to manage via GitOps
4. Default behavior: Should the controller auto-detect or have better error messages indicating the missing namespace configuration?