SCIM extensions support

[azmeuk]

pydantic-scim2 should be able to parse an EnterpriseUser payload and generate python objects accordingly. There should be some design about how to deal with extensions.

Maybe something based on __getitem__ would be nice?

user = User.model_validate(payload)
assert user[EnterpriseUser].employee_number == "1234"

Or something that would guess the models and implement an object inheriting from different bases:

user = User.model_validate(payload)
assert user.employee_number == "1234"
assert isinstance(user, User)
assert isinstance(user, EnterpriseUser)

Or maybe

user = User[EnterpriseUser](...)
user[EnterpriseUser].employee_number = "1234"