[ECS] [request]: Allow detailed configuration of metrics for Container Insights

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**Tell us about your request**
Make it possible to individually configure the metrics that are published when enabling Container Insights or Container Insights Enhanced mode. Ideally also allow to limit Dimensions.

**Which service(s) is this request for?**
This could be Fargate, ECS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
The number of metrics, dimension and dimension cardinality for Container Insights can quickly grow to pretty high numbers and therefore have a significant cost impact in CloudWatch.

Often only a subset of the metrics or Dimensions is actually needed for monitoring. With the ability to define (eg. per cluster) the published metrics, a cost efficient monitoring for Fargate / ECS would be possible.

**Are you currently working around this issue?**
* Switching off metrics and flying blind. Only enable when an issue comes up.

**Additional context**

* [Current Metrics with Container Insights](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Container-Insights-metrics-ECS.html)
* [Current Metrics with enhanced observability](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Container-Insights-enhanced-observability-metrics-ECS.html)

**Attachments**

The issue names no repository files, tests, or implementation entry points. Start by locating how this roadmap repository records ECS and Container Insights requests, then review the linked AWS metric documentation. Done would require a defined configuration approach for selecting metrics and limiting dimensions, along with an agreed implementation scope.

Written by the indexing model from the issue text.