Mandatory service extra selection

It will be more flexible for user to set whether the extras are mandatory or not. Include the option to set minimum or maximum selection required.

Use case:

  1. (Optional) After selecting a service, user may select up to 3 extra. He may select none.
  2. (Mandatory) After selecting a service, user MUST select minimum 1 extra, and up to 2.

Reference from Amelia: