(aws-ecs-patterns): unable to set DesiredCount to zero

The ApplicationLoadBalancedFargateService construct rejects an attempt to set a DesiredCount of zero, however this is valid and supported in the underlying `AWS::ECS::Service` resource.

Common use cases for this:
- I want to "suspend" a service, particularly if it's a headless consumer with background worker tasks.
- During development of a new cluster with a new image, I want to deploy the cluster and supporting infrastructure without attempting to start the Docker image, because I don't want a slow startup attempt, with multiple retries and a lengthly rollback of the entire cluster every time I debug an issue with the image starting up.

### Environment

- **CDK CLI Version :** 2.0.0-rc.21 (build f35f136)

### Other

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This is :bug: Bug Report

Start by locating the ApplicationLoadBalancedFargateService construct and the validation around DesiredCount, then compare its behavior with the underlying AWS::ECS::Service resource. Confirm that synthesizing a service with DesiredCount set to zero succeeds while existing positive values continue to work.

Written by the indexing model from the issue text.