feat: enable cert_manager, image_prepuller, kargo, jupyterhub, spark_operator, multi_acct on hub

Align hub addon set with main branch. These were disabled but are part
of the workshop platform:
- multi_acct: manages IAM role selectors for ACK EKS-managed capabilities
- cert_manager: certificate management (webhook dependency)
- image_prepuller: pre-pulls images for faster pod startup
- kargo: progressive delivery / promotion
- jupyterhub: ML notebooks
- spark_operator: Spark jobs

Author: allamand

gitops/overlays/environments/control-plane/enabled-addons.yaml

@@ -7,16 +7,16 @@ enabledAddons:
   metrics_server: true
   ingress_class_alb: true
   aws_load_balancer_controller: true
-  cert_manager: false
+  cert_manager: true
   external_secrets: true
   external_dns: true
   aws_efs_csi_driver: false
-  image_prepuller: false
+  image_prepuller: true
   # GitOps
   argo_events: true
   argo_rollouts: true
   argo_workflows: true
-  kargo: false
+  kargo: true
   flux: false
   # Security
   keycloak: true
@@ -38,7 +38,7 @@ enabledAddons:
   kro: false
   kro_manifests: false
   kro_manifests_hub: true
-  multi_acct: false
+  multi_acct: true
   platform_manifests: true
   backstage: true
   kubevela: true
@@ -53,11 +53,11 @@ enabledAddons:
   ack_dynamodb: false
   ack_efs: false
   # ML/AI
-  jupyterhub: false
+  jupyterhub: true
   kubeflow: false
   mlflow: false
   ray_operator: true
-  spark_operator: false
+  spark_operator: true
   airflow: false
   # AWS Resources (Crossplane-managed VPC secrets etc.)
   aws_resources: true