Add support for ephemeral storage configuration for Fargate tasks

[TimeToogo]

https://aws.amazon.com/about-aws/whats-new/2021/04/amazon-ecs-aws-fargate-configure-size-ephemeral-storage-tasks/

---

Enter [N/A] in the box, if an item is not applicable to your change.

Testing

• [x] Unit tests passed
• [ ] Integration tests passed
• [x] Unit tests added for new functionality
• [ ] Listed manual checks and their outputs in the comments (example)
• [ ] Link to issue or PR for the integration tests:

Documentation

• [ ] Contacted our doc writer
• [ ] Updated our README

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[phishy]

So I take it ephemeral storage is currently not supported in ecs-cli. Bummer.