Story
As an Image Updater user trying to deploy applications across clusters at scale, I want to Image Updater runs on the applications regardless where the applications are deployed. As the engineer works on this feature, we want to create a well thoughout design and get feedback/buy-ins from other senior level engineers.

Background and Approach
Currently, the Image Updater controller watches the local Kubernetes API for ImageUpdater CRs. In a multi-cluster setup, the Application is in a remote cluster, but the CR must be in the management cluster.

• The "Why": Users want to bundle the ImageUpdater CR inside the same Helm chart as their application.

• Technical Path: * Research the use of ArgoCD Cluster Secrets (labeled argocd.argoproj.io/secret-type: cluster) to discover target clusters.

• • Define the security model: How will the controller get permissions to watch CRs in remote namespaces?

• • Define the Controller Manager logic: Will it use a Manager per cluster or a multi-cluster cache?

• • Propose configuration flags (e.g., {}allowed-clusters{-} or -cluster-label-selector).

Out of Scope

• Implementation of the controller logic.

• Support for non-ArgoCD managed clusters.

Dependencies

• <Describes what this story depends on. Dependent stories and EPICs should be linked to the story.>

Acceptance Criteria (Mandatory)

• Create a design doc
• Present the proposal in Cabal
• Receive feedback by engineering team
• Address feedback 

Definition of Done

• Code Complete:
  • All code has been written, reviewed, and approved.
• Tested:
  • Unit tests have been written and passed.
  • Ensure code coverage is not reduced with the changes.
  • Integration tests have been automated.
  • System tests have been conducted, and all critical bugs have been fixed.
  • Tested and merged on OpenShift either upstream or downstream on a local build.
• Documentation:
  • User documentation or release notes have been written (if applicable).
• Build:
  • Code has been successfully built and integrated into the main repository / project.
  • Midstream changes (if applicable) are done, reviewed, approved and merged.
• Review:
  • Code has been peer-reviewed and meets coding standards.
  • All acceptance criteria defined in the user story have been met.
  • Tested by reviewer on OpenShift.
• Deployment:
  • The feature has been deployed on OpenShift cluster for testing.