Resolve "Add "What's new" menu item in top navigation"

What does this MR do?

This merge request adds a What's new link to the help dropdown in the top navigation.

What are the relevant issue numbers?

Closes #25341 (moved)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the style guides(https://about.gitlab.com/handbook/engineering/quality/test-engineering/).