Allow to set user defined workers role name (#496)

* Allow to set user defined workers role name

* Add changelog entry

* Keep single variable for worker role name

variables.tf

@@ -251,3 +251,9 @@ variable "manage_worker_iam_resources" {
   type        = bool
   default     = true
 }
+
+variable "workers_role_name" {
+  description = "User defined workers role name."
+  type        = string
+  default     = ""
+}