title: Add new configurable field of datetime type via system.xml
body: <p>I have a module and system.xml file inside my etc folder. I have added text fields and select box type configurable fields through this xml file.</p>
  
  <p>Now I need to add a new field which should show a date time picker and receive date time values in it.</p>
  
  <p>How can we achieve this?</p>