api: Use unthrottled email backend for Django Error Emails

[nils-wisiol]

Currently, error emails are in the slow lane

[peterthomassen]

See the email_backend argument at https://docs.djangoproject.com/en/dev/topics/logging/#django.utils.log.AdminEmailHandler Seems simple enough.

However, I'm not sure how to extend Django's default logging configuration with this setting, as opposed to overwriting it.