title: Enable floatingFilter in autoGroupColumn
body: <p>How to enable floatingFilter in autoGroupColumn's header cell?</p>
  <p>Seems like this is not enough:</p>
  <pre><code>autoGroupColumnDef: {
          resizable: true,
          cellClass: 'group-row-cell col-number-1',
          headerClass: 'head-number-1',
          cellRendererParams: {
              suppressCount: true
          },
          suppressMovable: true,
          floatingFilter: true
  }
  </code></pre>
  <p>All headers contain floating filter element except the autoGroupColumn</p>
  <p><a href="https://i.stack.imgur.com/xHHCA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xHHCA.png" alt="enter image description here" /></a></p>