Replace window.confirm with GlModal for registration token reset

What does this MR do and why?

This MR solves: #344124 (closed) it replaces the window confirm dialog with a GlModal for the runner registration token.

Screenshots or screen recordings

before	after

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. login in as root on you gdk
2. http://gitlab.localdev:3000/admin/runners
3. click on register an instance runner
4. click on reset registration token
5. see modal in action

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.