Fixed #22135 -- Added ModelAdmin.get_changeform_initial_data().

Allows custom behavior for setting initial form data in ModelAdmin.
By default, initial data is set via GET params. The new method allows
this behavior to be overridden.

Thanks egasimus for the suggestion.

tests/admin_views/admin.py

@@ -796,6 +796,10 @@ class RestaurantAdmin(admin.ModelAdmin):
     inlines = [WorkerInlineAdmin]
     view_on_site = False
 
+    def get_changeform_initial_data(self, request):
+        return {'name': 'overridden_value'}
+
+
 site = admin.AdminSite(name="admin")
 site.register(Article, ArticleAdmin)
 site.register(CustomArticle, CustomArticleAdmin)