title: Yii2 how add a new action button in grid
body: <p>I have following grid. </p>
  
  <pre><code>    $gridColumns = [
                  'class'=&gt;'kartik\grid\ActionColumn',
                  'headerOptions'=&gt;['class'=&gt;'kartik-sheet-style'],
                  'template' =&gt; '{delete}{my_button}', 
              ],
  
      echo GridView::widget([
              'dataProvider'=&gt; $dataProvider,
              'columns' =&gt; $gridColumns,
              'filterModel' =&gt; $filterModel,
              ],
          ]);
  </code></pre>
  
  <p>I want add to <code>template</code> a new action button for example <code>{my_button}</code>.</p>