Add DEFAULT_AUTO_FIELD to silence warning on the command line

[JackWilb]

Does this PR close any open issues?

No

Give a longer description of what this PR addresses and why it's needed

We were getting a bunch of warnings that look like:

...
api.Upload: (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 ApiConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
api.Workspace: (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 ApiConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
...

Following the advice here, I chose to set it to AutoField so we don't have more migrations to run.

Provide pictures/videos of the behavior before and after these changes (optional)

N/A

Are there any additional TODOs before this PR is ready to go?

No