title: AngularJS ui-grid change header template for expandableRows column
body: <p>I'd like to change the header of expandableRow Column in ui-grid, but I can't seem to figure out how.</p>
  
  <p><a href="https://i.stack.imgur.com/ZbDYj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZbDYj.png" alt="enter image description here"></a></p>
  
  <p>To be clear by the header I mean the circled plus in the image above.
  I'm hoping to use this header cell to put a different button there with an entire different functionality than what it currently does.</p>
  
  <p>I attempted to add my own columnDef with <code>field: "expandableRow"</code> and a <code>headerCellTemplate</code> but I got an error that I can't have duplicated fields (and it broke my grid). 
  I can't seem to find info on this in the docs, but maybe I missed it. Anyone know how I can add a template file to replace what's displayed in the cell above?</p>
  
  <p>EDIT: To clarify, I don't want to remove the column entirely like in the the other question suggested as a duplicate. I want to keep the column and the functionality of expanding the rows. I only want to change the expand all button which I've circled in the image above</p>