Design a comprehensive GitOps workflow using Argo CD or Flux for managing deployments in a Kubernetes production environment. The workflow must support multi-cluster management, automated rollback on deployment failure, and configuration drift detection. Explain how you would structure the repository (mono-repo vs poly-repo) and handle secrets management (integrating with Vault or Sealed Secrets). Detail the steps for a self-service developer experience where pushing to a specific branch triggers a dry-run and promotion to production.