Rename CLC files and favor Terraform list index syntax

* Rename Container Linux Config (CLC) files to *.yaml to align
with Fedora CoreOS Config (FCC) files and for syntax highlighting
* Replace common uses of Terraform `element` (which wraps around)
with `list[index]` syntax to surface index errors

google-cloud/container-linux/kubernetes/workers/workers.tf

@@ -78,7 +78,7 @@ data "ct_config" "worker-ignition" {
 
 # Worker Container Linux config
 data "template_file" "worker-config" {
-  template = file("${path.module}/cl/worker.yaml.tmpl")
+  template = file("${path.module}/cl/worker.yaml")
 
   vars = {
     kubeconfig             = indent(10, var.kubeconfig)