Add Copy to Clipboard Button to Review App Modal

Problem

The original MVC issue https://gitlab.com/gitlab-org/gitlab-ee/issues/10761 intended for a copy button to easily copy and paste the script that is needed into another place the be implemented in the merge request code. The copy button, however, did not make it into the scope of the MVC.

Further information

This is a follow-up issue to gitlab-ce#60988.

Solution

Once the button exists, we should add it in.