Enable Kubernetes aggregation by default

* Change `enable_aggregation` default from false to true
* These days, Kubernetes control plane components emit annoying
messages related to assumptions baked into the Kubernetes API
Aggregation Layer if you don't enable it. Further the conformance
tests force you to remember to enable it if you care about passing
those
* This change is motivated by eliminating annoyances, rather than
any enthusiasm for Kubernetes' aggregation features

Rel: https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/

aws/fedora-coreos/kubernetes/variables.tf

@@ -142,8 +142,8 @@ variable "enable_reporting" {
 
 variable "enable_aggregation" {
   type        = bool
-  description = "Enable the Kubernetes Aggregation Layer (defaults to false)"
-  default     = false
+  description = "Enable the Kubernetes Aggregation Layer"
+  default     = true
 }
 
 variable "worker_node_labels" {