Add Container Linux Config snippets feature

* Introduce the ability to support Container Linux Config
"snippets" for controllers and workers on cloud platforms.
This allows end-users to customize hosts by providing Container
Linux configs that are additively merged into the base configs
defined by Typhoon. Config snippets are validated, merged, and
show any errors during `terraform plan`
* Example uses include adding systemd units, network configs,
mounts, files, raid arrays, or other disk provisioning features
provided by Container Linux Configs (using Ignition low-level)
* Requires terraform-provider-ct v0.2.1 plugin

aws/container-linux/kubernetes/variables.tf

@@ -60,6 +60,18 @@ variable "worker_type" {
   description = "Worker EC2 instance type"
 }
 
+variable "controller_clc_snippets" {
+  type        = "list"
+  description = "Controller Container Linux Config snippets"
+  default     = []
+}
+
+variable "worker_clc_snippets" {
+  type        = "list"
+  description = "Worker Container Linux Config snippets"
+  default     = []
+}
+
 # bootkube assets
 
 variable "asset_dir" {