Add default_auto_field setting, strongly recommended in Django 3.2

[jaap3]

Without this Django issues the following warnings when running the tests:

System check identified some issues:

WARNINGS:
testprofiles.RequiredFieldUser: (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 AppConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
testprofiles.StandaloneUserModel: (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 AppConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
testprofiles.TestUser: (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 AppConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.

[peppelinux]

for future PR please ask to PR to dev branch ;)

[jaap3]

Ah sorry, I didn't realize there was a dev branch