New setting to define extra navigation links

[Zerotask]

Is it a third party application feature request?

No

Describe your feature request

We'd like to show all applications and models (SIDEBAR.show_all_applications) and define some extra navigation links before those (dashboard, show website, some external links, some custom sites etc). If you define those links in SIDEBAR.navigation, then it shows only those links but not show_all_applications. Therefore we suggest to add a new setting SIDEBAR.extend_navigation, to easily add new navigation links without the need to define every single app and model in the settings and just show them all.