title: Run pipeline on gitlab when branch is deleted
body: <p>Is it possible to run a pipeline thanks to Gitlab CI/CD after a branch is deleted.</p>
  <p>In fact I want to edit file after that branch is removed.</p>
  <p>For example, I have two repositories, R1 and R2.</p>
  <p>In R1 I have 2 branches</p>
  <ul>
  <li>B1</li>
  <li>B2</li>
  </ul>
  <p>I want to edit a file from R2 when B1 (which is a  R1's branch) is removed.</p>
  <p>I know how to access and edit the file but I don't know how can I set a trigger for removed branch.</p>