The Amazon Resource Name (ARN) of a task definition to use to update the Express Gateway service. This allows
you to manage your own task definition, giving you more control over the service configuration such as adding
sidecar containers.
The task definition must have a container named Main with a single TCP port mapping that
includes a container port and port name. The task definition must also have FARGATE
compatibility.
If you provide a task definition ARN, you cannot also specify primaryContainer,
taskRoleArn, cpu, or memory.