Make EKS Kubernetes version configurable via module variable

[Copilot]

The cluster_version variable in staging was defined but unused—the EKS module hardcoded kubernetes_version = "1.32".

Changes

• EKS module: Added kubernetes_version variable (defaults to "1.32")
• EKS module: Use var.kubernetes_version instead of hardcoded value
• Staging config: Pass local.cluster_version to module's kubernetes_version input

# infrastructure/staging/eks.tf
module "eks" {
  source = "../modules/eks"
  
  name               = "${local.env}-${local.cluster_name}"
  environment        = local.env
  kubernetes_version = local.cluster_version  # Now configurable
  # ...
}

The Kubernetes version is now configurable per environment while maintaining the same default behavior.

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