[ECS Optimized AMI] [request]: Release ECS Optimized AMI for sa-east-1 region

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**Tell us about your request**
The ECS Optimized AMI is not yet available for the sa-east-1 region, even though ARM instances are available since 12/2020.
This is keeping us from updating some of the instances we have there.

**Which service(s) is this request for?**
ECS / EC2 / AMI

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Our deployment scripts (using CDK) depends on the ECS Optimized AMI being available in the region of the deployment.
It gets the image id from the parameter store and then creates the instances using it.
Since the AMI is not available for the sa-east-1 region, the script fails there.

**Are you currently working around this issue?**
We are still using m5 instances for sa-east-1, to avoid the issue, because the AMI is correctly provided for non-ARM instances.

No repository files, tests, or entry points are mentioned. Start by reviewing the ECS Optimized AMI availability for sa-east-1 and the related EC2 parameter-store path. Done means the ARM ECS Optimized AMI is released and available through the expected regional parameter.

Written by the indexing model from the issue text.