Additional changes required to make fields optional

[Comeani]

I realized while working on getting the user creation from the admin account creation tool to work properly that the initial changes I made to the User model were not sufficient to actually have the requests be well defined supplying just the user name.

This PR allows for the fields to be blank in addition to no longer being required, and importantly adjusts the signatures for UserManager.create_user and UserManager.create_superuser so they are assumed to be in extra_fields instead of being positional arguments.

[Comeani]

This will need to be in place for pitt-crc/sam_scripts#35 to work properly.

[djperrefort]

See blank vs null:

https://docs.djangoproject.com/en/5.0/ref/models/fields/#null

[Comeani]

I see, so blank is for validation in forms where null governs whether the database value can be null or an empty string.

So we want it to be OK to be null here so the requests with just the username are accepted, but blank should remain false as when it comes a user (or us on their behalf) making changes to their "user profile" values, first name/last name/email should be "required" fields before they can save any changes?

[Comeani]

@djperrefort So it turns out using str | None as the type for the inputs to create_user still caused them to be required positional arguments (at least when creating super users). Because the method for setting up the values passed into create_user when creating super users is deeper to django (and doesn't default to providing None as the argument), I think this is the simplest way to do it. The best alternative outright would be to just have my POSTs of user data include those other fields with an empty value, which I will probably need to do for passwords anyways.