Expose a few more configurable items and add input validators

variable.region.tf

@@ -1,6 +1,9 @@
 variable "region" {
   description = "The region where the droplet will be created"
-  default     = "nyc3"
   type        = string
-}
 
+  validation {
+    condition     = can(regex("^[a-z]{3}[0-9]$", var.region))
+    error_message = "The region must be a valid DigitalOcean region format (e.g., nyc3, sfo3)."
+  }
+}