[Compability] Changes to AutoField with Django 3.2

[ckoerber]

Description

With the new Django 3.2 version, makemigrations and migrate seem to raise a warning about AutoFields for the notification app.

WARNINGS:
notifications.Notification: (models.W042) Auto-created primary key used when not defining a primary key type, by default 'django.db.models.AutoField'.
	HINT: Configure the DEFAULT_AUTO_FIELD setting or the NotificationsConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.

To Reproduce

This happens on default when installing the most recent Django version 3.2

pip install Django==3.2
espressodb startproject temp
cd temp
python manage.py migrate

Additional context

Django 3.2 release notes: https://docs.djangoproject.com/en/3.2/releases/3.2/

When defining a model, if no field in a model is defined with primary_key=True an implicit primary key is added. The type of this implicit primary key can now be controlled via the DEFAULT_AUTO_FIELD setting and AppConfig.default_auto_field attribute. No more needing to override primary keys in all models.

Maintaining the historical behavior, the default value for DEFAULT_AUTO_FIELD is AutoField. Starting with 3.2 new projects are generated with DEFAULT_AUTO_FIELD set to BigAutoField. Also, new apps are generated with AppConfig.default_auto_field set to BigAutoField. In a future Django release the default value of DEFAULT_AUTO_FIELD will be changed to BigAutoField.

[ckoerber]

It seems to me that the least intrusive way of fixing this is adding the default_auto_field attribute to the NotificationsConfigApp to point to 'django.db.models.AutoField' or maybe even BigAutoField. Since existing projects use AutoField, I am tending to this one to not cause new migrations for all existing projects. I will implement and test this.