[Fargate] [request]: Add procstat level metrics to ECS container metadata

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**Tell us about your request**

What do you want us to build?
Add proctstat level metrics to ECS container metadata. Currently, I see these metrics present on the Task metadata endpoint: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-metadata-endpoint-v4.html. I was wondering if there's a way we can extract other data like num_fds or num_threads which is present at the process level.

**Which service(s) is this request for?**
Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I'm trying to extract procstat level data from the Fargate task to see the number of open file handles currently present in the container. I see there's a Cloudwatch agent that we can install to collect that data here: https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch-Agent-procstat-process-metrics.html, But I was hoping I could do the same via ECS container metadata than installing another agent on the task.

**Are you currently working around this issue?**
I haven't solved this problem yet.

**Additional context**
None.

**Attachments**
None.

Start by reviewing the ECS task metadata endpoint v4 documentation and the linked CloudWatch Agent procstat process-metrics documentation. Determine how process-level values such as num_fds and num_threads could be exposed through ECS container metadata; the request is complete when the intended procstat metrics are available without installing another agent.

Written by the indexing model from the issue text.