fun getProductAccess(userToken: TokenResponse, userId: String, productId: String): Call<ApiContainer<ProductAccess>>
Checks whether the user has access to the given product.
userId - The user's ID, must match the one in the token
userToken - The user's access token
productId - The product's ID to check (e.g. specific newspaper)
Return
On success it will return if the user has access, failure if something went wrong or the user doesn't have access