fix(aws_ecs): Do not output NetworkConfiguraiton to ECS Service when using EXTERNAL deployment controller (#26338)

When using an external deployment controller, ECS Service creation fails because the `NetworkConfiguration` is output to the template.
This fix prevents the output of `NetworkConfiguration` when using external deployment controller.

Closes #26335

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: msysh

packages/@aws-cdk-testing/framework-integ/test/aws-ecs/test/fargate/integ.external-deploy-controller.js.snapshot/aws-ecs-integ.assets.json

@@ -0,0 +1,19 @@
+{
+  "version": "32.0.0",
+  "files": {
+    "08f603b34dd592b1fe18725d57edf629a7b88639b2b9e032676b44567f62a470": {
+      "source": {
+        "path": "aws-ecs-integ.template.json",
+        "packaging": "file"
+      },
+      "destinations": {
+        "current_account-current_region": {
+          "bucketName": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}",
+          "objectKey": "08f603b34dd592b1fe18725d57edf629a7b88639b2b9e032676b44567f62a470.json",
+          "assumeRoleArn": "arn:${AWS::Partition}:iam::${AWS::AccountId}:role/cdk-hnb659fds-file-publishing-role-${AWS::AccountId}-${AWS::Region}"
+        }
+      }
+    }
+  },
+  "dockerImages": {}
+}