[FireLens] [request]: Feature Request: Human readable container name from FireLens ECS metadata

### Community Note

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**Tell us about your request**
When ECS metadata is turned on, Firelens attaches some extra ECS metadata to each log line. However this metadata does not include the human readable container name, only an autogenerated container name:

```
{
"container_id": "957b36352863d2af06fa223f73e8e2f26d900c3f12ba81bc4df58c9e390a9a4d",
"container_name": "/ecs-chattersubscriptionsubscriptiontaskdefinition84AF3B49-39-app-d0c89395d3efaac05200",
"ec2_instance_id": "i-0e8c1703f57233826",
"ecs_cluster": "chatter-base-ClusterEB0386A7-A8Q2H6M4RI1I",
"ecs_task_arn": "arn:aws:ecs:us-east-1:209640446841:task/chatter-base-ClusterEB0386A7-A8Q2H6M4RI1I/56a8667e7a454b0a8c7a39d5723de11e",
"ecs_task_definition": "chattersubscriptionsubscriptiontaskdefinition84AF3B49:39",
"log": "REDACTED",
"source": "stderr"
}
```

Ideally there would be a human readable container name taken from the ECS task definition as well, for easier querying

**Which service(s) is this request for?**
FireLens, ECS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I would like to be able to more easily query logs in Cloudwatch Insights, without needing to resort to a regex query to extract the human readable container name from the autogenerated name field

**Are you currently working around this issue?**
Regex in the CWI query

Start by reviewing the FireLens and ECS metadata behavior described in the issue, including the current autogenerated container_name and the ECS task definition. Done means the emitted log metadata also includes a human-readable container name from the task definition, so CloudWatch Insights queries no longer require regex extraction.

Written by the indexing model from the issue text.