title: How to retrieve dropdown items from an observable?
body: <p>How would you retrieve dropdown items from an observable in <code>@rxweb/reactive-dynamic-forms</code> ? </p>
  
  <p>how do you inject service in <code>FormControlConfig</code> subclass? shared code here <a href="https://stackblitz.com/edit/angular-bs5yqt-nmzcwj" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-bs5yqt-nmzcwj</a></p>