Switch the UI for toggling new MR draft status to be a checkbox

What does this MR do and why?

For #358437 (closed)

Switch the text/link button for dynamically changing to/from Draft status to be a checkbox with additional help text.

Screenshots or screen recordings

Before (text link button)	After (checkbox)
mark-as-draft-checkbox-before	mark-as-draft-checkbox-after

How to set up and validate locally

1. Begin the process of creating a new MR
2. Select a source/target to reach the main editing form
3. Toggle the draft status / edit the title to have / not have "Draft:" included

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.