Add horizontal scrolling to all sub-navs on mobile viewports

What does this MR do?

Adds horizontal scrolling to all the sub navigation on mobile views. This was previously only available on the repository tab (commits page).

Are there points in the code the reviewer needs to double check?

Perhaps a better way to refactor out the common haml code

Why was this MR needed?

Adding it to all to keep the UI consistency and to offer mobile users a better interface

What are the relevant issue numbers?

Closes #20779 (closed)

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together