Merge PR to allow target groups to be passed into ASG

[bhechinger]

To allow for ingress we need load balancers that are attached to the ASG used to manage the ECS cluster.

I had attempted to do this with aws_autoscaling_attachment but the behavior of that resource is really strange and it wasn't working.

This allows one to provide the list of target groups directly to the ASG which is a much more reliable mechanism.