added db_admin variable with appropriate validation block

Author: andrefaria24

main.tf

@@ -10,7 +10,7 @@ resource "random_password" "master" {
 resource "aws_rds_cluster" "aurora_pg" {
   cluster_identifier      = "aurora-${var.db_name}"
   engine                 = "aurora-postgresql"
-  master_username        = "admin"
+  master_username        = var.db_admin
   master_password        = random_password.master.result
   database_name          = var.db_name
   skip_final_snapshot    = true

variables.tf

@@ -3,6 +3,15 @@ variable "db_name" {
   type        = string
 }
 
+variable "db_admin" {
+  description = "Database admin username"
+  type = string
+  validation {
+    condition = !contains("admin")
+    error_message = "Database administrative username must not be admin"
+  }
+}
+
 variable "region" {
   description = "AWS Region"
   type        = string