Migrate AWS ECS apps to ECS Express

[marcoieni]

Amazon recently launched ECS Express, which promises to reduce the amount of terraform code you need to write to provision a service (at no additional cost).

We should try to migrate our apps, starting from the simplest ones to that and see if it would be beneficial to us.

[amustaque97]

The best time to pick this task is probably sometime next week, based on the comment hashicorp/terraform-provider-aws#45219 (comment).