Management task to minimise saved data of old members

One-sentence description

Management task to minimise saved data of old members.

Desired behaviour

We should have a management task that can remove all data of old members (address, phone number, birthday, bank account etc) that we do not need anymore after the expiration of their membership. This task should then be run on March 1, according to the new privacy policy (#648 (closed))

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information