Document spec.sourceNamespaces as required field for EKS ArgoCD capability

[yuwesu]

Summary

The spec.sourceNamespaces field is a required field when using the EKS ArgoCD capability, but this requirement is not currently documented in the ArgoCD Projects guide.

Problem

Users may encounter errors or unexpected behavior when creating AppProjects without specifying spec.sourceNamespaces, as this field is mandatory for the EKS capability. More detail could refer Argo CD upstream document.

Proposed Solution

Add a new subsection in the "Project configuration" section that documents:

• spec.sourceNamespaces is a required field for EKS ArgoCD capability
• Default value should include the argocd namespace
• Additional namespaces must be added if Applications or ApplicationSets are created in other namespaces

Suggested Placement

Insert the new "Source namespaces" subsection after "Source repositories" and before "Destination restrictions" in the Project configuration section.

Additional Context

This documentation gap affects users implementing multi-namespace ArgoCD deployments with EKS capabilities.