[ECS] [request]: compute optimizer for ECS

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**Tell us about your request**
Figuring out the right memory and CPU configuration for each service and task running inside of ECS is a bit of black magic. It would be nice if ECS offered a feature which would monitor your tasks for you and provide suggestions for improvements (reducing or increasing memory and CPU settings) so that your clusters could run more efficiently. Kind of like the [Compute Optimizer](https://aws.amazon.com/compute-optimizer/) launched recently for EC2.

**Which service(s) is this request for?**
ECS (but I don't see why it couldn't work for EKS, Fargate, etc)

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We run almost 1000 services in ECS, and the choice of CPU and memory settings are often picked once and never adjusted (unless the app is crashing with OOM or similar). I recently came across a large application which was only using about 25% of its provisioned memory settings (based on RSS vs. task memory limit). We can set up monitoring and alerting in Datadog or Cloudwatch to try to alert and react to these, but it would be great if AWS made it easy to find your most over (or under) provisioned tasks and services and gave suggestions for what they should be set to.

**Are you currently working around this issue?**
Manual review.

**Additional context**
None.

**Attachments**

Here's an example of how overprovisioned the application I mentioned was: