mockData

cars = [
     {
        "id": "dc9e722d-4b24-5f6a-82ff-a71f937c62c0",
        "brand": "FERRARI",
        "model": "Portofino",
        "type": "Sportiva",
        "price": "195000",
        "discount": 12,
        "image1": "",
        "image2": "",
        "image3": ""
      },
    {...}, etc...
]

users = [
     {
        "id": "7c3ef3d3-f86d-50f9-8b85-b48a40cc772f",
        "firstName": "Sabina",
        "lastName": "Fadel",
        "username": "SabinFad",
        "password": "SabinFad",
        "email": "SabinFad@.email.com",
        "CarsForSale": [
          {
            "id": "dc9e722d-4b24-5f6a-82ff-a71f937c62c0",
            "brand": "FERRARI",
            "model": "Portofino",
            "type": "Sportiva",
            "price": "195000",
            "discount": 12,
            "image1": "",
            "image2": "",
            "image3": ""
          },
          {...}, etc...
        ]
]

//risultato voluto:
[
    {carId:"dc9e722d-4b24-5f6a-82ff-a71f937c62c0",
    userId:7c3ef3d3-f86d-50f9-8b85-b48a40cc772f,
    username:'SabinFad',
    brand:'FERRARI',
    model:'Portofino,
    etc...},
    {etc..}...
]