Add confirm_danger_modal component

What does this MR do and why?

Related to #254274 (closed) and #342115 (closed) this MR will begin the process to migrate the confirm_danger_modal away from bootstrap to a gl-modal

This MR:

• Replaces the .js-confirm-danger* classes with .js-legacy-confirm-danger
• Adds a vue.js confirm_danger button and modal component

Screenshots or screen recordings

There are no visual changes in this MR, existing pages that use this confirmation modal will be updated in subsequent MRs.

How to set up and validate locally

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

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.