AWS ECS support

[h3poteto]

I want to use ex_aws for AWS ECS.

There was a pull request: #385
But it is closed, and there is no available service for ECS: https://github.com/ex-aws?q=service&type=&language=

[Doerge]

I recently had success with using this package for it: https://github.com/davepersing/ex_aws_ecs although it was a limited use case.

[h3poteto]

I knew it, and sometimes I'm using Upptec/ex_aws_ecs.

davepersing/ex_aws_ecs is published to hex.pm, but that API is insufficient; therefore, I'm using Upptec/ex_aws_ecs. But in any case they are not officially supported libraries. I hope that ex_aws officially supports AWS ECS.