Support aws_appautoscaling_policy for ECS Service

[mattthaber]

Description

From what it looks like, ecs_service costs are solely calculated by Usage Hours* desired_count, however typically when using ecs with autoscaling, one will setup the resource to be

resource "aws_appautoscaling_target" "service" {
  max_capacity       = var.max_count
  min_capacity       = var.min_count
  resource_id        = "service/cluster/${aws_ecs_service.service.name}"
  scalable_dimension = "ecs:service:DesiredCount"
  service_namespace  = "ecs"
}

resource "aws_ecs_service" "service" {
  desired_count = # whatever

  lifecycle {
    ignore_changes = [ desired_count ]
  }
}

in which you ignore the desired_count completely, and just have variables for min/max.

It would be nice to support aws_appautoscaling_target for ecs in the usage file like other services with aws_appautoscaling_*

I do know one easy workaround is just set desired_count = var.max_count but because you typically lifecycle ignore desired_count, it is very easy to not setup services as such.