chore: [WIP] 🍰 Refactor Maintenance Page

Created by: Tirokk

🍰 Pullrequest

• I refactored the maintenance page.
  • And I added a webapp page to test the maintenance page, because it is kind of impossible to develop it with docker, because of leak of automatic recompiling.
  • Test the maintenance page in webapp logged in with http://localhost:3000/testing-in-webapp/maintenance.
    • This is working …

Issues

• fixes #4116

Todo

• But with docker-compose up http://localhost:5000 it doesn’t work. Investigate why.