In this exercise what I'd like you to do is:
1. Add the formArrayName directive to the div on line 17, binding it to subjects
2. Also on line 17, Iterate over subjects and add an index
3. On the input on line 20, bind the formControlName directive to the index
4. Update the addSubject() method in the component to add a new FormControl to subjects
Exercise Link: https://stackblitz.com/fork/rxngforms-fa-template-exercise