Rename basic abstractions from Fargate to ECS to change the Fargate driver into an ECS driver

What does this MR do?

This is the first MR necessary to change the Fargate driver into a ECS driver. More specifically, the scope of this MR is:

• Rename Fargate adapter abstraction into ECS adapter abstraction
• Move cmd/fargate/commands/custom files to cmd/ecs/commands/custom
• Rename struct in config.go from Fargate to ECS

Important: despite this MR changes a significant number of files, it is basically variables and files renaming.

Why was this MR needed?

This is necessary to transform the Fargate driver into an ECS driver.

Are there points in the code the reviewer needs to double check?

N/A

Does this MR meet the acceptance criteria?

• Documentation created/updated - should be handled in a separated MR
• Added tests for this feature/bug
• In case of conflicts with master - no conflicts

What are the relevant issue numbers?