[ECS] [request]: Metrics for fargate containers using service discovery

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**Tell us about your request**
Metrics for Fargate containers which use service discovery and not load balancer

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
When any container is attached to the load balancer(internal/internet), we get metrics such as total request count, number of 4xx and 5xx, average latency etc. We would like the same metrics to be available for the fargate containers using service discovery instead of load balancer.

**Are you currently working around this issue?**
No workarounds so far

**Additional context**
The containers could be public or private.

The issue names no repository files, tests, or implementation entry point. Start by reviewing how metrics are provided for load-balanced Fargate containers and how service discovery applies across Fargate, ECS, and EKS. Done would require an agreed approach for request count, 4xx/5xx, and latency metrics for service-discovery containers.

Written by the indexing model from the issue text.