[web] Add possibility for the navigation-panel to be horizontal

Summary:
issue: https://linear.app/comm/issue/ENG-2739/move-navigationpanel-from-the-sidebar-to-a-top-bar
When AppSwitcher (that uses NavigationPanel underneath) is used in the Topbar it'll need to be horizontal. The tabs will also have to display differently. But the SettingSwitcher (that also uses NavigationPanel underneath) is supposed to stay as it is.

Test Plan: Pass horizontal={true} to NavigationPanel.Container in AppSwitcher and check that it displayes correctly.

Reviewers: przemek, bartek, michal, tomek

Reviewed By: bartek, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6343