title: how to listen of angular template driven form changes
body: <p>in my form:</p>
  
  <pre><code>&lt;form&gt;
     &lt;label class="form-check-label"&gt;
       &lt;input [(ngModel)]="options.o1" name="o1"
              type="checkbox" class="form-check-input" &gt;
       Option 1
     &lt;/label&gt;
     &lt;label class="form-check-label"&gt;
       &lt;input [(ngModel)]="options.o2" name="o2"
              type="checkbox" class="form-check-input" &gt;
       Option 2
     &lt;/label&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>I want to be informed whenever one of the two checkboxes is changed, not by adding an event handler to each of the checkboxes but by adding an event handler to the form, in reality there are much more fields in the form.</p>