[ECS] [request]: Support UpdateContainerAgent API for ECS-Optimized Amazon Linux 2 AMI (arm64)

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**Tell us about your request**
(Created this issue from a customer's issue) Currently, the [UpdateContainerAgent API](https://docs.aws.amazon.com/cli/latest/reference/ecs/update-container-agent.html) is not supported for ECS Optimized AMI with arm64 architecture, but only supported for ECS Optimized AMI with amd64 architecture. Request is to support this API for the arm64 AMI so customer can use it to update the ECS Agent on the instance ( https://docs.aws.amazon.com/AmazonECS/latest/developerguide/agent-update-ecs-ami.html).

**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?**
Update ECS agent on Amazon ECS-optimized Amazon Linux 2 (arm64) AMI. The fact that the UpdateContainerAgent API is not supported for arm64 AMI makes this process harder than other ECS Optimized Linux AMI.

**Are you currently working around this issue?**
Workaround is to follow https://docs.aws.amazon.com/AmazonECS/latest/developerguide/manually_update_agent.html to manually update the agent by running shell commands on the instance.

**Additional context**
N/A

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

Start by reviewing the UpdateContainerAgent API documentation and the ECS agent update guidance linked in the issue, then compare the supported amd64 and ECS-Optimized Amazon Linux 2 arm64 paths. Done means the API supports updating the ECS agent on the arm64 AMI instead of requiring the documented manual shell-command workaround.

Written by the indexing model from the issue text.