Add dynu_root_domain variable for domain import flow

infrastructure/terraform/dynu/variables.tf

@@ -1,3 +1,10 @@
+
+variable "dynu_root_domain" {
+  description = "Dynu root domain name to reconcile/import (for example: lan.ddnsgeek.com)."
+  type        = string
+  default     = "lan.ddnsgeek.com"
+}
+
 variable "dynu_api_key" {
   description = "Dynu API key/token used by the Dynu Terraform provider."
   type        = string