[ECS] [request]: Support Cross Service Cross Task Definition Dependency

**Tell us about your request**
What do you want us to build?
Support Cross Service Cross Task Definition Dependency

**Which service(s) is this request for?**
Fargate, ECS

Based on aws documentation https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_definitions.html,

"Your entire application stack does not need to exist on a single task definition, and in most cases it should not. Your application can span multiple task definitions by combining related containers into their own task definitions, each representing a single component"

This means that it is best practice to separate each component/service into its own task definition. However, cross task definition is not yet supported. Only container dependencies within a single task definition is supported. This needs extending to support cross service.

Start by reviewing the AWS ECS task definitions documentation linked in the issue and the distinction between Fargate and ECS services. Define what cross-service, cross-task-definition dependency support would mean and how completion could be verified; the issue names no repository files, tests, or implementation entry points.

Written by the indexing model from the issue text.