Add helpful messages to empty wiki view

What does this MR do?

Adds helpful messages to the empty wiki view.

Notes:

• Closes #38919 (closed)
• Includes a fresh gitlab.pot
• Commits will be squashed on merge

Why was this MR needed?

#38919 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#38919 (closed)