Api: Manage privacy policy

[ElSalvo96]

We need to manage the privacy policy.

• Add to table user a new flag, privacy policy and market
• Return it on user object
• Add a new endpoint called like "accept privacy policy", add here the creation of user object

[marcomoratto98]

Because it was only the add-on of a flag i used the same branch for the task #29.
The endpoint is reachable by the path "api/User/acceptprivacy" and is a Post method, even if it doesn't need a body.