Create a merger mechanism to composite the collection's graph data with the one from the DB.

## 🎉 Description

When we introduced the pagination and filters to the `/collections` endpoint, we added the option to filter by status. The problem here is that the `approved` ones can only be retrieved from the graph, so we had to move the fetch before getting the db data. A proper solution will be to create a merger mechanism that fetch both the graph and db data and then consolidates (or hydrates the graph data with the db one).

* [ ] 🐛 This is a bug report.
* [X] 📈 This is a feature request.