title: Set no tab as default active tab on mat tab
body: <p>I have search functionality implemented using <code>mat-tab</code>, I need no tab selected on initial load.
  Tab should get active only when user clicks on specific tab.</p>
  
  <p>Currently, first tab is active on load.
  I have tried setting <code>selectedIndex="null"</code> but didn't work.
  Also, I need reset the selected tab on a button click.</p>
  
  <p><a href="https://i.stack.imgur.com/sUndp.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sUndp.jpg" alt="Search using mat tab"></a></p>