Define default_auto_field to silence Django 3.2+ warnings

[blag]

tos.TermsOfService: (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 TOSConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
tos.UserAgreement: (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 TOSConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.

It's an easy fix.

[nicholasserra]

Thanks! This didn't trigger a new migration?

[blag]

It didn't for me, because Django previously silently defaulted to using AutoField. This change just makes the default explicit. If a user specifies DEFAULT_AUTO_FIELD in their settings.py it will override this one.

If I had switched it to BigAutoField I think it would have triggered a migration. I considered that, but I'll leave that to users to figure out if they need that or not and set in DEFAULT_AUTO_FIELD if so.

[nicholasserra]

Sounds right, thank you!