Refresh instances in autoscaling group when launch configuration changes

* Changes to worker launch configurations start an autoscaling group instance
refresh to replace instances
* Instance refresh creates surge instances, waits for a warm-up period, then
deletes old instances
* Changing worker_type, disk_*, worker_price, worker_target_groups, or Butane
worker_snippets on existing worker nodes will replace instances
* New AMIs or changing `os_stream` will be ignored, to allow Fedora CoreOS or
Flatcar Linux to keep themselves updated
* Previously, new launch configurations were made in the same way, but not
applied to instances unless manually replaced

aws/flatcar-linux/kubernetes/workers/workers.tf

@@ -22,6 +22,14 @@ resource "aws_autoscaling_group" "workers" {
     var.target_groups,
   ])
 
+  instance_refresh {
+    strategy = "Rolling"
+    preferences {
+      instance_warmup        = 120
+      min_healthy_percentage = 90
+    }
+  }
+
   lifecycle {
     # override the default destroy and replace update behavior
     create_before_destroy = true