US 048 - Follow a user profile Backend

[rubensituuh]

• [x] Add followed users list to user model
• [x] Provide the list of followed users when providing the user profile information
• [x] Provide the list of followers users when providing the user profile information
• [x] Implement the logic to show the followers
• [x] Create the logic to follow a User
• [ ] Create post in the view "GetUserByUsername"
• [ ] Add followed and following users list to user model