title: how to create a gitlab bot to automate issues handling
body: <p>We're working on a few project hosted on Gitlab and it would be really convenient for us to have a bot to automate some issues handling.<br />
  E.g.: automatically close issues that have been tagged as 'waiting answer from client' more than 20 days ago</p>
  <p>I can't find any guide nor tutorial on how doing this, i don't even know if it could be done entirely in github or do i need to create my bot from an external service.</p>