feature-request: "paginate" method should be added to model relations

To use it like:

```
currentUser.posts.paginate...
```

The issue requests adding a `paginate` method to model relations in the RailwayJS framework. Start by examining the existing pagination plugin code and how model relations are defined. Look for where relation methods are added to models. The goal is to implement a paginate method that works on a relation like `currentUser.posts.paginate(...)`. Check if there are existing tests for pagination or relations to understand the expected behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.