fix: show dock_to_right only if nav sidebar is enabled

[SukiCZ]

When AdminSite.enable_nav_sidebar is set to False, Django will hide the sidebar (here) which also applies to Unfold just fine.

The issue is the icon dock_to_right is still visible and when user is on a change view, the icon moves the submit buttons (in bottom-right corner) out of the screen.

This PR will show dock_to_right only if nav sidebar is enabled.
Fixes: #943

[lukasvinclav]

From Django docs:

https://docs.djangoproject.com/en/5.1/ref/contrib/admin/#django.contrib.admin.AdminSite.enable_nav_sidebar

The docs are saying that variable enable_nav_sidebar controls if the sidebar is displayed on larger screens. In your code you are only controlling display of the toggle button.

[SukiCZ]

Yes, control of the nav bar is done here already. The only issue IS the icon.

See comment here in Issue #943 .