title: "required" validator for p-calendar
body: <p>There is no required validator available for p-calendar control of PrimeNG:</p>
  
  <pre><code>&lt;p-calendar formControlName="startDateControl" [minDate]="today" showIcon="true"&gt;&lt;/p-calendar&gt;
  </code></pre>
  
  <p>Is there any workaround?</p>