Add validation that requires atleast one user specified

cloud/aws/s3_bucket/inputs.tf

@@ -17,4 +17,8 @@ variable "users" {
   type        = list(string)
   default     = []
   description = "List of users to generate S3 API keys for. Will be used as the IAM name."
+  validation {
+    condition     = length(var.users) > 0
+    error_message = "At least one user must be specified!"
+  }
 }