fix: use correct default value for nat gateway setup

This should be true by default, because the only case in which private nodes are not provisioned is
if the user explicitly sets the count to 0.

src/deploy.rs

@@ -89,7 +89,7 @@ impl TestnetDeployer {
             setup_nat_gateway: options
                 .private_node_vm_count
                 .map(|count| count > 0)
-                .unwrap_or(false),
+                .unwrap_or(true),
             tfvars_filename: options.environment_type.get_tfvars_filename(&options.name),
             uploader_vm_count: options.uploader_vm_count,
             uploader_vm_size: options.uploader_vm_size.clone(),