Add missing authorizations app for commonground-api-common

[SonnyBA]

Fixes makemigrations creating a new migration for several authorization models.

Changes
The migrations that are currently generated when running makemigrations in open-klant generates a migration with models for the authorizations app because the migrations in the existing app are not recognized (as the app is not in the INSTALLED_APPS)

See https://github.com/maykinmedia/commonground-api-common/blob/1.12.1/docs/quickstart.rst?plain=1#L43.
Also see the check_migrations CI job that encountered this issue.

[stevenbal]

@SonnyBA come to think of it, I'm actually not sure if all components use this (e.g. Objects/Objecttypes), so wouldn't it be better to add this only to the components that need it? 🤔

[SonnyBA]

Open-zaak (commonground-api-common used the middleware class from this project), Open-Klant and Open-Notificaties use the authorizations app from commonground-api-common.

I think the migrations authorizations migrations currently are recognized (even if the app is not installed) because the middleware.py imports them. It should be easily fixed though whenever we move the authorization related middleware to the authorizations app. This probably requires a new release though of OAF (because all projects pull in commonground-api-common through OAF) and commonground-api-common.

The current suggested fix is probably a bit less work but is also the uglier solution. @Coperh @stevenbal which option would you prefer?