[ecs] [console]: More informative error message when unable to create a new revision of task definition

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**Tell us about your request**
When I tried to create a new revision of task definition using ECS console, console only returned the following error message, which is not informative for troubleshooting the issue:

` "Unable to create a new revision of Task Definition mytaskdef:101"`

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

**Are you currently working around this issue?**
Check the detailed error message in CloudTrail "RegisterTaskDefinition" event to figure out that the IAM role lacks the required permissions, for example

`"errorMessage": "User: arn:aws:sts::0123456789:assumed-role/test/testuser is not authorized to perform: iam:PassRole on resource: arn:aws:iam::0123456789:role/arn:aws:iam::0123456789/role/admin"`

Start by reviewing the ECS console task-definition revision flow and the RegisterTaskDefinition event in CloudTrail, using the reported iam:PassRole failure as the example. Determine how the console receives and surfaces this failure. Done means an unsuccessful revision creation reports a useful underlying permission error instead of only the generic message.

Written by the indexing model from the issue text.