[service] [request]: Ability to set custom session name for task role

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**Tell us about your request**
This request was submitted on behalf of a customer
Cx wants to set a session name for the assumed task role in order to better track user actions on containers via CloudTrail.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
The ability to set a session name for the assumed task role in order to better track user actions on containers via CloudTrail. Currently, tasks assume the task role and the session ID is the task ID. This makes it difficult to track CloudTrail Api calls on a user basis.

**Are you currently working around this issue?**
Yes. Created a trust policy that explicitly allows the role to assume itself. User will then access the container and assume the task role specifying the RoleSessionName (manual/doesn't scale well).

**Additional context**
N/A

**Attachments**
N/A

The request identifies ECS task roles, RoleSessionName, and CloudTrail as the relevant entry points, but names no repository files or tests. Start by confirming how ECS currently derives the task-role session ID and the constraints on custom names; done means an agreed ECS capability that supports user-level CloudTrail tracking.

Written by the indexing model from the issue text.