Allow changes to "runner_worker.max_jobs" for Docker Autoscaler

Remove ignore_changes from the ASG for Docker Autoscaler.  The reasoning
described in the comment was poor; min_size and desired_capacity are fixed
at zero, so won't change, and max_size should change when runner_worker.max_jobs
is changed, and will not cause immediate scale-up.
If it causes scale-down, this the logical desired behaviour.

Author: jonmcewen

docker_autoscaler.tf

@@ -187,13 +187,4 @@ resource "aws_autoscaling_group" "autoscaler" {
       propagate_at_launch = true
     }
   }
-
-  lifecycle {
-    # do not change these values as we would immediately scale up/down, which is not wanted
-    ignore_changes = [
-      desired_capacity,
-      min_size,
-      max_size
-    ]
-  }
 }