docs: Correct Karpenter variable references for changes made in v20.0 (#2900)

Author: its-nihal

modules/karpenter/README.md

@@ -66,8 +66,8 @@ module "karpenter" {
 
   cluster_name = module.eks.cluster_name
 
-  create_iam_role = false
-  iam_role_arn    = module.eks.eks_managed_node_groups["initial"].iam_role_arn
+  create_node_iam_role = false
+  node_iam_role_arn    = module.eks.eks_managed_node_groups["initial"].iam_role_arn
 
   # Since the nodegroup role will already have an access entry
   create_access_entry = false