BO17 - Create a DAL function to add a Sponsorship level

[gregoriopalama]

Add a DAL function in the Sponsorship API.

The function should accept the informations about the sponsorship level:

• name. This is required;
• position: this will be checked. If there is an other sponsorship level with the same position, the other one will be updated and moved to the next position, and the same will be done for any other level with a colliding position. This field is optional. If not provided, the position will be set to the actual number of sponsorship levels in the db (index must start from 0).

The response will be an errore if something goes wrong. Otherwise, the function will provide the inserted sponsorship level object, including the ID of the document in the DB.