title: How to show total in ag-grid header
body: <p>How can I show total in header?</p>
  <p>For example, I want to show sum of age as <strong>Age(x)</strong></p>
  <p><a href="https://i.stack.imgur.com/zCwXS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zCwXS.png" alt="enter image description here" /></a></p>