🗃️(contacts) rename base to override

To improve code readability, I propose to rename
the contact field `override`. This comes along
with the fact a contact should not not always
override another (it's the case were I only want
to create some personal contacts).

src/backend/core/admin.py

@@ -194,7 +194,7 @@ class ContactAdmin(admin.ModelAdmin):
     list_display = (
         "full_name",
         "owner",
-        "base",
+        "override",
     )