Swappable Model support for Group Model

[Vasanth]

When dealing with custom groups there are two ways of extending the model

1. Create a separate "GroupExtension" model and define an OneToOne relationship to the Group model
2. Inherit the default Group Model into a new CustomGroup model

Since my current project uses object-level permission (django-guardian) everywhere and quite a few additional fields I decided to go along with option 2. However, I quickly found that the Group model is not swappable in the same manner as the user model.

Trying to implement it manually has further let me down the rabbit hole where I found that libraries have hardcoded dependency onto the Group model directly. This makes working with custom group models quite hard.

It'd be great if the the group model can also be defined in the settings which can then be leveraged by all libraries to provide a smoother dev experience working with Custom Group and permissions

For reference my current user and group looks something like,

class CustomGroup(Group):
    additional_field = models.CharField(max_length=10)
    ....

class CustomUser(AbstractBaseUser, PermissionsMixin):
    groups = models.ManyToManyField(CustomGroup)
    ....

[Mariusz Felisiak]

Duplicate of #29748.