Fix scroll bug in OnyxNavBar mobile mode when you have too many NavItems

[MajaZarkova]

• [x] When we have too many nav buttons in mobile mode of the nav bar and the screen is not high enough a scrollbar should appear.
• [x] add 2rem to max width of mobile nav items
• [x] Adjust mobile context menu to be able to scroll
  • [x] app version changes: same optics as nav items (just not clickable).
  • [x] Fix duplicate border in mobile context menu
  • [x] Screenshot test is missing -> https://github.com/SchwarzIT/onyx/pull/1540
  • [x] create UX "adjust" ticket for the mobile app version

  • 1552

• [x] fix mobile nav parent highlighting
  • [x] parent is hidden if parent is not clickable -> add storybook example
  • [x] in the drilled-down level, the parent should not be highlighted if a child is active

[BoppLi]

For review, show

• overflowing menu content
  • open menu: it now scrolls with many nav buttons
  • open "Item 2": it scrolls with many nav items/children
  • open context menu:
  • it scrolls on many context options
  • the app version is not sticky anymore
  • there are no double borders between options
• updated Storybook example
  • Item 2 is not highlighted when opened, only its active child is highlighted
  • Item 3 is hidden when opened