text: Title: How to add error message when `UNIQUE constraint failed`
  Body: when import twice get a long `Traceback (most recent call last):`
  ```py
  class Employee(models.Model):
    id_number = models.CharField(max_length=180, null=True, blank=True, unique=True)
  ```
   
  I want to show the error like admin default error message, like `already exist Employee with this _id_number `