Migrate from individual Applications to ApplicationSet pattern

[Copilot]

Refactored ArgoCD application management from individual Application manifests to an ApplicationSet that auto-discovers directories with kustomization.yaml files.

Changes:

• Created application-set/application-set.yaml using git directory generator with path: "*" pattern
• Converted all component application.yaml files to kustomization.yaml with helmCharts fields
• Enabled --enable-helm in ArgoCD's kustomize.buildOptions ConfigMap patch
• Added explicit namespace resources for cert-manager and cnpg
• Removed root kustomization.yaml (no longer needed)

Before:

# Root kustomization.yaml
resources:
  - cert-manager/application.yaml
  - cnpg/application.yaml
  # ... 7 more explicit references

After:

# application-set/application-set.yaml
generators:
  - git:
      directories:
        - path: "*"

Same 9 applications deployed (argocd, cert-manager, cnpg, cnpg-barman-cloud-plugin, kube-prometheus-stack, loki, opentelemetry-collector, startsch, tempo) with identical versions and configurations. ApplicationSet skips directories without kustomization.yaml (application-set, monitoring).

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