docs: update ECS service and Fargate documentation for new AZ rebalancing default values (#35156)

Updates documentation to reflect ECS change in default behavior for the
`AvailabilityZoneRebalancing` property:

- For create service requests, when no value is specified for
AvailabilityZoneRebalancing, Amazon ECS defaults to ENABLED if the ECS
service is compatible with AvailabilityZoneRebalancing. If the ECS
service is not compatible with AvailabilityZoneRebalancing, Amazon ECS
defaults to DISABLED.
- For update service requests, when no value is specified for
AvailabilityZoneRebalancing, Amazon ECS defaults to the existing
service’s AvailabilityZoneRebalancing value. If the service never had an
AvailabilityZoneRebalancing value set, Amazon ECS treats this as
DISABLED.

### Issue # (if applicable)

Closes #<issue number here>.

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### Description of changes

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### Description of how you validated changes

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### 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: djglaser

packages/aws-cdk-lib/aws-ecs/lib/ec2/ec2-service.ts

@@ -96,7 +96,7 @@ export interface Ec2ServiceProps extends BaseServiceOptions {
    * service must not be a target of a Classic Load Balancer.
    *
    * @see https://docs.aws.amazon.com/AmazonECS/latest/developerguide/service-rebalancing.html
-   * @default AvailabilityZoneRebalancing.DISABLED
+   * @default AvailabilityZoneRebalancing.ENABLED
    */
   readonly availabilityZoneRebalancing?: AvailabilityZoneRebalancing;
 }

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

@@ -71,7 +71,7 @@ export interface FargateServiceProps extends BaseServiceOptions {
    * of a Classic Load Balancer.
    *
    * @see https://docs.aws.amazon.com/AmazonECS/latest/developerguide/service-rebalancing.html
-   * @default AvailabilityZoneRebalancing.DISABLED
+   * @default AvailabilityZoneRebalancing.ENABLED
    */
   readonly availabilityZoneRebalancing?: AvailabilityZoneRebalancing;
 }