title: Django - Using a different email backend for admin error emails
body: <p>I'm using a custom email backend in my Django application (CeleryEmailBackend in this case):</p>
  
  <pre><code>EMAIL_BACKEND = 'djcelery_email.backends.CeleryEmailBackend'
  </code></pre>
  
  <p>My logging configuration:</p>
  
  <pre><code>LOGGING = {
      # ...
      'handlers': {
          'mail_admins': {
              'level': 'ERROR',
              'filters': ['require_debug_false'],
              'class': 'django.utils.log.AdminEmailHandler',
      },
      # ...
  }
  </code></pre>
  
  <p>The Admin error emails also get sent by the same email backend.<br>
  So if there is a problem with the email backend (e.g. Celery is not running). Then I won't receive the server error emails.</p>
  
  <p>Is there a way to make <code>AdminEmailHandler</code> use a custom email backend?</p>