fix(ecs): ecs exec cannot be enabled for ECS Anywhere (ecs.ExternalService) (#31374)

### Issue # (if applicable)

Closes #31181.

### Reason for this change

In the `ecs.ExternalService` class (ECS Anywhere), the `enableExecuteCommand` property cannot be set to true, so it is not possible to enable ECS exec.
However, the [documentation](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-exec.html) states that ECS Anywhere supports ECS Exec.

> ECS Exec is supported for tasks that run on the following infrastructure:
> Linux and Windows containers on external instances (Amazon ECS Anywhere)



### Description of changes
Remove unnecessary if statement.



### Description of how you validated changes
Fix an unit test.



### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: mazyu36

packages/aws-cdk-lib/aws-ecs/README.md

@@ -1174,10 +1174,10 @@ const taskDefinition = new ecs.Ec2TaskDefinition(this, 'TaskDef');
 taskDefinition.addContainer('TheContainer', {
   image: ecs.ContainerImage.fromRegistry('example-image'),
   memoryLimitMiB: 256,
-  logging: ecs.LogDrivers.awsLogs({ 
+  logging: ecs.LogDrivers.awsLogs({
     streamPrefix: 'EventDemo',
     mode: ecs.AwsLogDriverMode.NON_BLOCKING,
-    maxBufferSize: Size.mebibytes(25), 
+    maxBufferSize: Size.mebibytes(25),
   }),
 });
 ```
@@ -1606,7 +1606,7 @@ to work, you need to have the SSM plugin for the AWS CLI installed locally. For
 [Install Session Manager plugin for AWS CLI](https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html).
 
 To enable the ECS Exec feature for your containers, set the boolean flag `enableExecuteCommand` to `true` in
-your `Ec2Service` or `FargateService`.
+your `Ec2Service`, `FargateService` or `ExternalService`.
 
 ```ts
 declare const cluster: ecs.Cluster;
@@ -1771,9 +1771,9 @@ const service = new ecs.FargateService(this, 'Service', {
 ## ServiceManagedVolume
 
 Amazon ECS now supports the attachment of Amazon Elastic Block Store (EBS) volumes to ECS tasks,
-allowing you to utilize persistent, high-performance block storage with your ECS services. 
-This feature supports various use cases, such as using EBS volumes as extended ephemeral storage or 
-loading data from EBS snapshots. 
+allowing you to utilize persistent, high-performance block storage with your ECS services.
+This feature supports various use cases, such as using EBS volumes as extended ephemeral storage or
+loading data from EBS snapshots.
 You can also specify `encrypted: true` so that ECS will manage the KMS key. If you want to use your own KMS key, you may do so by providing both `encrypted: true` and `kmsKeyId`.
 
 You can only attach a single volume for each task in the ECS Service.

packages/aws-cdk-lib/aws-ecs/lib/external/external-service.ts

@@ -105,10 +105,6 @@ export class ExternalService extends BaseService implements IExternalService {
       throw new Error ('Cloud map options are not supported for External service');
     }
 
-    if (props.enableExecuteCommand !== undefined) {
-      throw new Error ('Enable Execute Command options are not supported for External service');
-    }
-
     if (props.capacityProviderStrategies !== undefined) {
       throw new Error ('Capacity Providers are not supported for External service');
     }

packages/aws-cdk-lib/aws-ecs/test/external/external-service.test.ts

@@ -237,6 +237,39 @@ describe('external service', () => {
     });
   });
 
+  test('with enableExecuteCommand set to true', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'MyVpc', {});
+    const cluster = new ecs.Cluster(stack, 'EcsCluster', { vpc });
+    addDefaultCapacityProvider(cluster, stack, vpc);
+    const taskDefinition = new ecs.ExternalTaskDefinition(stack, 'TaskDef');
+
+    taskDefinition.addContainer('web', {
+      image: ecs.ContainerImage.fromRegistry('amazon/amazon-ecs-sample'),
+      memoryLimitMiB: 512,
+    });
+
+    // WHEN
+    new ecs.ExternalService(stack, 'ExternalService', {
+      cluster,
+      taskDefinition,
+      enableExecuteCommand: true,
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::ECS::Service', {
+      TaskDefinition: {
+        Ref: 'TaskDef54694570',
+      },
+      Cluster: {
+        Ref: 'EcsCluster97242B84',
+      },
+      LaunchType: LaunchType.EXTERNAL,
+      EnableExecuteCommand: true,
+    });
+  });
+
   test('throws when task definition is not External compatible', () => {
     const stack = new cdk.Stack();
     const vpc = new ec2.Vpc(stack, 'MyVpc', {});
@@ -306,30 +339,6 @@ describe('external service', () => {
 
   });
 
-  test('error if enableExecuteCommand options provided with external service', () => {
-    // GIVEN
-    const stack = new cdk.Stack();
-    const vpc = new ec2.Vpc(stack, 'MyVpc', {});
-    const cluster = new ecs.Cluster(stack, 'EcsCluster', { vpc });
-    addDefaultCapacityProvider(cluster, stack, vpc);
-    const taskDefinition = new ecs.ExternalTaskDefinition(stack, 'TaskDef');
-
-    taskDefinition.addContainer('web', {
-      image: ecs.ContainerImage.fromRegistry('amazon/amazon-ecs-sample'),
-      memoryLimitMiB: 512,
-    });
-
-    // THEN
-    expect(() => new ecs.ExternalService(stack, 'ExternalService', {
-      cluster,
-      taskDefinition,
-      enableExecuteCommand: true,
-    })).toThrow('Enable Execute Command options are not supported for External service');
-
-    // THEN
-
-  });
-
   test('error if capacityProviderStrategies options provided with external service', () => {
     // GIVEN
     const stack = new cdk.Stack();