Feature: upload a document anonymously

[C4ptainCrunch]

This is a suggestion for the workshop on the 16/11/2022, please don't assign it to yourself or work on it before this date, it is intended as an exercise for the participants.

Context: some users want to upload their documents but don't want their name to appear on DocHub.

UI proposal: We could add a checkbox in the upload form that the user can check if they want an anonymous upload

Implementation proposal (spoiler alert)

• A: make document.user nullable and store null as the user for anonymous uploads and update the templates to display the null value (if we do this, it's irreversible, so add a warning on the checkbox)
• B: add a new anonymous field on document and add a condition to the templates to hide the user in the interface (if we do this, also add the checkbox on the edit form so it can be reversed)