Enhancement: Separate Reviewer and FactChecker users with unique permissions in the backend

### Background Information

Currently, in Aletheia, there are three user types in `ability.decorator.ts`, one of which is FactChecker, used for both reviewers and fact-checkers with the same permissions in the backend. The goal of this issue is to separate them and assign different permissions, as is already done in the frontend.

### Steps to Reproduce

I believe we should separate the two users, Reviewer and FactChecker, and discuss which permissions each will have. Currently, both have permission to create and update.


### How

The best way to achieve this should be discussed.

### Expected Behavior

Ambos users existirem em backend e terem permissões unicas, acredito que dessa forma não precisando definir essas permissões em frontend