Support for EKS Managed Node Groups (#602)

* Finished first cut of managed node groups

* Updated formatting and extra fields.

* Updating Changelog and README

* Fixing formatting

* Fixing docs.

* Updating required Version

* Updating changelog

* Adding example for managed node groups

* Managed IAM Roles for Nodegroups now have correct policies. Tags can now be added to node groups.

* Fixing bug where people could set source_security_group_ids without setting ssh key causing a race condition within the aws provider.

* Adding lifecycle create_before_destroy

* Adding random pet names for create_before_destroy

* Updating per comments.

* Updating required versions of terraform

* Updating per comments.

* Updating vars

* Updating minimum version for terraform

* Change worker_groups_managed_node_groups to node_groups

* Using for_each on the random_pet

* Adding changes recommended by @eytanhanig

* Update node_groups.tf

variables.tf

@@ -293,3 +293,9 @@ variable "attach_worker_cni_policy" {
   type        = bool
   default     = true
 }
+
+variable "node_groups" {
+  description = "A list of maps defining node group configurations to be defined using AWS EKS Managed Node Groups. See workers_group_defaults for valid keys."
+  type        = any
+  default     = []
+}