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

docs/plugins/development/staged-changes.md

@@ -0,0 +1,42 @@
+# Staged Changes
+
+!!! danger "Experimental Feature"
+    This feature is still under active development and considered experimental in nature. Its use in production is strongly discouraged at this time.
+
+!!! note
+    This feature was introduced in NetBox v3.4.
+
+NetBox provides a programmatic API to stage the creation, modification, and deletion of objects without actually committing those changes to the active database. This can be useful for performing a "dry run" of bulk operations, or preparing a set of changes for administrative approval, for example.
+
+To begin staging changes, first create a [branch](../../models/extras/branch.md):
+
+```python
+from extras.models import Branch
+
+branch1 = Branch.objects.create(name='branch1')
+```
+
+Then, activate the branch using the `checkout()` context manager and begin making your changes. This initiates a new database transaction.
+
+```python
+from extras.models import Branch
+from netbox.staging import checkout
+
+branch1 = Branch.objects.get(name='branch1')
+with checkout(branch1):
+    Site.objects.create(name='New Site', slug='new-site')
+    # ...
+```
+
+Upon exiting the context, the database transaction is automatically rolled back and your changes recorded as [staged changes](../../models/extras/stagedchange.md). Re-entering a branch will trigger a new database transaction and automatically apply any staged changes associated with the branch.
+
+To apply the changes within a branch, call the branch's `commit()` method:
+
+```python
+from extras.models import Branch
+
+branch1 = Branch.objects.get(name='branch1')
+branch1.commit()
+```
+
+Committing a branch is an all-or-none operation: Any exceptions will revert the entire set of changes. After successfully committing a branch, all its associated StagedChange objects are automatically deleted (however the branch itself will remain and can be reused).