chore: Explicitly set default auto field

[heindrickdumdum0217]

https://docs.djangoproject.com/en/5.0/ref/settings/#default-auto-field

Users may set DEFAULT_AUTO_FIELD to django.db.models.BigAutoField in settings. In that case, it will create an additional migration file which updates APIRequestLog table id to BigAutoField. And it's causing problem during the migration in each deployment and testing with tox.

If we explicitly set default_auto_field in app config, we can avoid unexpected migration.