User profile feature: Setting (Interaction only between friends)

as a log-in user, I want to only interact with my friends rather than strangers, so that I can share privately.

technical details

• in user profile page, there will be a setting button, it will open a setting pop up window for user
• in setting pop up window, user can select "communicate only with followed user" button to prevent strangers comment
• user can undo the privacy setting