title: Add combobox in extjs grid for only one row
body: <p>I have an extjs grid which shows data from a store. The last column is always empty except for the entry in store where, a flag <code>is_deleted=0</code>(Only one entry will have is_deleted=0). I have to show a combobox for this entry with values edit and delete.</p>
  
  <p>The current grid code I have is as follows:</p>
  
  <pre><code>Ext.define('TasoDesktop.view.taso.popups.accountComments.AccountCommentsGrid', {
  extend: 'Ext.grid.GridPanel',
  alias: 'widget.tasoAccountCommentsGrid',
  
  title: 'Previous Comments',
  
  initComponent: function () {
      this.store = 'AccountLevelComments';
  
      this.columns = [
          { header: 'Date Entered', dataIndex: 'modified_dt', flex: 0},
          { header: 'Comment', dataIndex: 'c_comment', flex: 0 },
          { header: 'Entered by', dataIndex: 'sid', flex: 0 },
          { header: 'Expiry Date', dataIndex: 'valid_until_dt', flex: 0 },
          { header: 'Action', flex: 0 }
      ];
  
      this.height = 400;
      this.width = 900;
  
      this.viewConfig = {
          stripeRows: true
      };
  
      this.autoScroll = true;
  
      this.callParent(arguments);
  }
  });
  </code></pre>
  
  <p>Only one of the Action column( with is_deleted = 0 in the store) should have the combo-box. How should I include the combobox for it based on the store value?</p>