Closes #10851: New staging mechanism (#10890)

* WIP

* Convert checkout() context manager to a class

* Misc cleanup

* Drop unique constraint from Change model

* Extend staging tests

* Misc cleanup

* Incorporate M2M changes

* Don't cancel wipe out creation records when an object is deleted

* Rename Change to StagedChange

* Add documentation for change staging

netbox/extras/choices.py

@@ -182,3 +182,20 @@ class WebhookHttpMethodChoices(ChoiceSet):
         (METHOD_PATCH, 'PATCH'),
         (METHOD_DELETE, 'DELETE'),
     )
+
+
+#
+# Staging
+#
+
+class ChangeActionChoices(ChoiceSet):
+
+    ACTION_CREATE = 'create'
+    ACTION_UPDATE = 'update'
+    ACTION_DELETE = 'delete'
+
+    CHOICES = (
+        (ACTION_CREATE, 'Create'),
+        (ACTION_UPDATE, 'Update'),
+        (ACTION_DELETE, 'Delete'),
+    )