[BATCH] [request]: Support AWS Systems Manager parameters instead of AMI IDs in ec2Configuration imageIdOverride

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**Tell us about your request**
When creating a Compute Environment we can specify an override for the AMI. Launch templates allow you to specify an SSM parameter instead of an AMI ID (https://docs.aws.amazon.com/autoscaling/ec2/userguide/using-systems-manager-parameters.html). It would be useful if we could do this in Batch so that we can centrally manage the AMI for multiple compute environments.

Now SSM Parameters can be shared across accounts this would be very useful to centrally manage the AMI across an organization.

**Which service(s) is this request for?**
Batch on EC2

**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 centrally manage the AMI used by compute environments.

**Are you currently working around this issue?**
API calls to discover and modify every compute environment

This request targets Batch on EC2 compute environments and the ec2Configuration imageIdOverride, with AWS Systems Manager parameters as the alternative to AMI IDs. Start by reviewing the linked Launch Templates documentation and the existing API-based workaround. Done means compute environments can centrally resolve a shared SSM parameter for their AMI override, including parameters shared across accounts.

Written by the indexing model from the issue text.