Unable to create rack reservations

[austind]

Environment

• Python version: 3.12.7
• Nautobot version: v2.3.11b1
• nautobot-design-builder version: 2.1.0

Expected Behavior

This should work:

rack_reservations:
  - rack: "{{ rack }}"
    user__name: admin
    description: Power Shelf
    units:
      - 4
      - 5
      - 6

Observed Behavior

Job fails with the following trace:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/celery/app/trace.py", line 477, in trace_task
    R = retval = fun(*args, **kwargs)
                 ^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/celery/app/trace.py", line 760, in __protected_call__
    return self.run(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/source/nautobot/extras/jobs.py", line 1136, in run_job
    result = job(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^
  File "/source/nautobot/extras/jobs.py", line 149, in __call__
    return self.run(*args, **deserialized_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design_job.py", line 250, in run
    return self._run_in_transaction(dryrun, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/contextlib.py", line 81, in inner
    return func(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design_job.py", line 355, in _run_in_transaction
    raise ex
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design_job.py", line 316, in _run_in_transaction
    self.implement_design(context, design_file, not dryrun)
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design_job.py", line 216, in implement_design
    self.environment.implement_design(design, commit)
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 831, in implement_design
    raise ex
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 815, in implement_design
    self._create_objects(self.model_map[key], value)
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 892, in _create_objects
    model = model_class(self, model_instance)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 591, in __init__
    self._update_fields()
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 620, in _update_fields
    setattr(self, field_name, value)
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/fields.py", line 204, in __set__
    setter()
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/fields.py", line 191, in setter
    model_instance = self._get_instance(obj, value)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/fields.py", line 179, in _get_instance
    value = obj.design_metadata.create_child(related_model, value, relationship_manager)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/nautobot_design_builder/design.py", line 321, in create_child
    model_class = self.environment.model_class_index[model_class]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
KeyError: <class 'nautobot.users.models.User'>

Steps to Reproduce

1. Create a Design Builder job
2. Try to create a rack reservation

[austind]

Issue appears to be related to this line, which excludes the users model.