Update admin topic page

What does this MR do and why?

• Align header with other pages.
• Migrate Empty State component.
• Align new topic form with others (remove hr and gray background for actions)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to http://gdk.test:3000/admin/topics
2. If you have some topics, try to search for something like testtesttest
3. See empty state
4. Click [New topic]
5. See the form

#457239 (closed)