[Feature] Match types between the frontend and backend

[dimitur2204]

Is your feature request related to a problem? Please describe.
Update the types of the campaign
There are wrong typings on the campaign such as:
campaign.beneficiary.person is not required on backend, but type safe on the frontend.

Describe the solution you'd like
Check out the backend schema and updates all the types accordingly.

Production broke, because of an issue we didn't manage to catch, which should have been easily catchable at buildtime 😕!

[kachar]

Let's link this task to #658