Dynamically add container(s) to container_definitions

[nbcchen]

Is your request related to a new offering from AWS?

Is this functionality available in the AWS provider for Terraform? See CHANGELOG.md, too.

• No 🛑: please wait to file a request until the functionality is avaialble in the AWS provider
• Yes ✅: please list the AWS provider version which introduced this functionality

Is your request related to a problem? Please describe.

Add container based on condition

Describe the solution you'd like.

container_definitions = {
  app = {
    image = "..."
  }
}

additional_containers = flatten(var.create_sidecar ? [
  {
    image = "..."
  }
]: [])

Describe alternatives you've considered.

Additional context