Based on our new design specs we want to replace default browser
behavior with our Pajamas Design System.

This required us to replace the confirm with a modal confirm.
GlModal information can be found here:
https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-modal--default

This was not currently feasible so this work is built on top of
a new JS Confirm Modal that will be pulled into its own MR.
The issue tracking that info can be found here:
https://gitlab.com/gitlab-org/gitlab/issues/205900