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/models/extras/branch.md

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+# Branches
+
+A branch is a collection of related [staged changes](./stagedchange.md) that have been prepared for merging into the active database. A branch can be mered by executing its `commit()` method. Deleting a branch will delete all its related changes.
+
+## Fields
+
+### Name
+
+The branch's name.
+
+### User
+
+The user to which the branch belongs (optional).

docs/models/extras/stagedchange.md

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+# Staged Changes
+
+A staged change represents the creation of a new object or the modification or deletion of an existing object to be performed at some future point. Each change must be assigned to a [branch](./branch.md).
+
+Changes can be applied individually via the `apply()` method, however it is recommended to apply changes in bulk using the parent branch's `commit()` method.
+
+## Fields
+
+!!! warning
+    Staged changes are not typically created or manipulated directly, but rather effected through the use of the [`checkout()`](../../plugins/development/staged-changes.md) context manager.
+
+### Branch
+
+The [branch](./branch.md) to which this change belongs.
+
+### Action
+
+The type of action this change represents: `create`, `update`, or `delete`.
+
+### Object
+
+A generic foreign key referencing the existing object to which this change applies.
+
+### Data
+
+JSON representation of the changes being made to the object (not applicable for deletions).

docs/plugins/development/staged-changes.md

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+# 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).