Migrate milestone labels GlCard to CrudComponent

What does this MR do and why?

• Migrate milestone labels GlCard go CrudComponent (see #476988 for more details)
• Update burndown chart banner text

Screenshots or screen recordings

Before	After

How to set up and validate locally

Project > plan > milestones > milestone > labels tab

Links

• ✂️ UX Paper Cuts 17.3 → Dark mode - Design Support (#452231 - closed)
• Migration: GlCard (gl-new-card variant) to Crud (#476988)
• ✂️ UX Paper Cuts 17.4 → Comments & system notes (#469616 - closed)