Uplift pni tristate fields

[Pomax]

Builds on #3757 and uplifts all NullBoolean fields to Boolean(null=True) (new recommended way to do things), save the four fields that needed to become the new ExtendedYesNoField (Yes/No/Unknown/Not applicable).

New code for this PR only: a8f3ba1 + 7510170

Related issues: #3729

One thing that we probably want to make sure works is running this on top of staging data, locally. This runs "from scratch" (using inv docker-new-env) but the more important question is whether these migrations won't break when presented with staging's data and schema

[Pomax]

@cadecairos I've added you for review mostly because I'm also touching some of the factory stuff, so making sure that all looks fine will help out a lot!

[kristinashu]

Awesome! I've check-off what has been done in the spreadsheet.

[cadecairos]

no issues with the changes. Copied staging locally and applied the migrations without any issue, and the pni page looks fine afterwards. Let's try this on staging!

[Pomax]

\o/

[Pomax]

these are all NullBoolean to Boolean(null=True) updates

[Pomax]

this change makes sure we use a Product based on the database schema, not what's in models.py (since models.py can change in the future, and then this migration would crash...)

[Pomax]

so this is a four stage uplife:

1. build new fields, with unique names, that use the new 4-state field type
2. migrate the 3-state data from the old fields as 4-state data to the new fields
3. delete the old fields
4. rename the new fields so they use the names of the old fields

This means that at the end of this migrations, nothing has really changed except the fields types got changed from NullBoolean to ExtendedYesNo, and some of the fields got renamed as per the spreadsheet

[mmmavis]

Code makes sense to me and works well locally. 👍