[ECS] [AWS CloudMap] [request]: ECS UpdateInstanceHealthStatus very slow to CloudMap

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**Tell us about your request**
ECS Fargate should update the the new CloudMap instance to healthy before deregister the old CloudMap instance

**Which service(s) is this request for?**
ECS Fargate, AWS CloudMap

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

Steps to reproduce:

1. Running 1 task of ECS Fargate with Service Discovery and container health check propagation configured
2. Update Fargate Service
3. When the new task become HEALTHY, the old instance gets deregistered from AWS CloudMap, yet it is faster than ECS update the health status of the new instance to CloudMap
4. This results in a short period of time where there is no healthy instance for this service, causing downtime during CD

Currently this is not an issue if I have more than 1 instance, the health status can alternate so that I always have healthy instances.
But this is an issue if I only have 1 desired instance.