Add clean user deletion to API documentation

[YetAnotherGerrit]

As a programmer that wants to delete users via API I am referenced to the GUI option of adding a data privacy deletion task, but there is no API documentation for the /api/v1/data_privacy endpoint.

[ralf401]

@YetAnotherGerrit there are some endpoints not covered in the documentation, see e.g. here.

Do you see a need for having this privacy deletion task covered? If so, what about the others which are missing? It could be argued that the users should use the UI instead of the API for safety reasons... But I'm open to add this, for sure.

[YetAnotherGerrit]

I don't think we need to fully document /api/v1/data_privacy, but at least on how to create a user deletion task. Because this is a very common requirement for admins that build their own user sync bridge.

Maybe also add a clue that it also may be an option to set users to inactive instead.