Dive in the possibility to use outputs to improve vars validation

[ianaya89]

Example:

output "validate_cidr_and_availability_zones_length" {
  value = length(var.eks_public_cidr)

  precondition {
    condition     = length(var.eks_public_cidr) == length(var.eks_availability_zones)
    error_message = "The length of eks_public_cidr (${length(var.eks_public_cidr)}) must match the length of eks_availability_zones (${length(var.eks_availability_zones)})."
  }
}