[ECS-Fargate] [request]: Document Cloudwatch rule and ECS Task Behavior

I have found that when triggering an ECS task from a Cloudwatch rule cron, if the task is already running, it does not create another instance/container of the task, even though the ECS task time started is updated to the time the rule executed. This is on Fargate Platform version 1.4. Per issue #232 I think the concurrency of ECS Fargate Tasks should be documented as it is not clear. Or there should be singleton and concurrent task types, although creating a Service seems to clarify some of this as you can create desired number of task instances. AWS Batch is a solution for some use cases and Step Functions (State Machine) for others.

I am currently implementing a Step Function for my use case. At a minimum the behavior of Cloudwatch Rule ECS Task trigger seems to need documentation.

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Start by reviewing the reported CloudWatch rule ECS task trigger behavior on Fargate platform version 1.4 and the related discussion in issue #232. Confirm whether an already-running task prevents a new task instance, then document the observed concurrency behavior and how Services, AWS Batch, or Step Functions relate to the use case.

Written by the indexing model from the issue text.