title: How to add a select-all chekbox to Column Header in Ag-Grid React?
body: <p>In Ag Grid, there is an option to add a checkbox to a row to select it. This can be defined in columnDefinitions as follows:</p>
  <pre><code>{
     checkboxSelection: true
  }
  </code></pre>
  <p>This checkbox is added on the row itself. Now my question is, how to add a select-all checkbox in the column header itself?</p>