feat: Add support for addon configuration_values (#2345)

Resolves undefined

examples/eks_managed_node_group/main.tf

@@ -64,6 +64,13 @@ module "eks" {
     vpc-cni = {
       most_recent              = true
       service_account_role_arn = module.vpc_cni_irsa.iam_role_arn
+      configuration_values = jsonencode({
+        env = {
+          # Reference docs https://docs.aws.amazon.com/eks/latest/userguide/cni-increase-ip-addresses.html
+          ENABLE_PREFIX_DELEGATION = true
+          WARM_PREFIX_TARGET       = 1
+        }
+      })
     }
   }