Fixes: #18863 - Exempt MPTT-based models from centrally applying ordering on querysets

[bctiemann]

Fixes: #18863

Because MPTT-based models rely on an implicit hierarchical ordering behavior, the central ordering of querysets of these models as introduced in #18729 causes its own unpredictability when using list views (which should preserve the hierarchical presentation). This includes models such as Region, ContactGroup, TenantGroup, etc.

This change identifies these models through checking model._meta.local_managers and exempts them from having order_by reapplied during list views in the API and UI.

[arthanson]

As the code is getting more complicated, can this be put into a Mixin that is included in both places so we centralize the code?

[bctiemann]

Because get_queryset takes a request in one place and not the other, and because the classes both have long inheritance trees already and the MRO causes a new mixin to just make things more confusing, I ended up deciding a util function was the best place for this logic to live. Open to suggestions of better organizational ideas, but at least now the redundancy is minimized.