Add extra confirmation window when converting shared CI runners to specific CI runners
Description
It is fairly easy to convert a shared CI runner to a specific CI runner. This is a one way transaction which can have a large negative impact if it wasn't intended.
Proposal
Add a modal window notification when switching a shared runner to specific runner further highlighting that this action cannot be undone, are you sure you want to do this.
Links / references
Originally referenced here: https://gitlab.com/gitlab-org/gitlab-ce/issues/34827#note_34467586