ECS-task Feature Request: Auto-setup IAM for read/write on a data bucket

[aaronsteers]

Since most of our use cases for ECS tasks will require read-write access to one or more buckets, it would greatly streamline the design work if IAM permissions could automatically granted to one ore more optionally-provided S3 buckets. When provided, the task role would be granted access to the bucket(s) without having to manage this externally from the module.