Roles endpoints

[Mateusz-Dobrzynski]

Create endpoints for managing roles (Admin and Organizer only):

• POST /user/{user_id}/tournament/{tournament_id}/roles – for creating new roles,
• GET/PATCH/DELETE /user/{user_id}/tournament/{tournament_id}/roles/{roles_id}

Testing:

• Grant a role to a user account that doesn't have any. Check whether the user is now permitted to perform appropriate operations.
• Check if user.get_roles() yields newly acquired roles.