Attempting to create a BarGauge panel with orientation="auto" raises an exception

[jwalgran]

What you expected to happen?

I can generate JSON for a dashboard with a BarGauge panel with orientation set to auto.

What happened?

Attempting to create a BarGauge panel with orientation="auto" raises an exception when running the dashboard code through generate-dashboard

Traceback (most recent call last):
  File "/Users/jwalgran/.pyenv/versions/3.8.10/bin/generate-dashboard", line 8, in <module>
    sys.exit(generate_dashboard_script())
  File "/Users/jwalgran/.pyenv/versions/3.8.10/lib/python3.8/site-packages/grafanalib/_gen.py", line 242, in generate_dashboard_script
    run_script(generate_dashboard)
  File "/Users/jwalgran/.pyenv/versions/3.8.10/lib/python3.8/site-packages/grafanalib/_gen.py", line 80, in run_script
    sys.exit(f(sys.argv[1:]))
  File "/Users/jwalgran/.pyenv/versions/3.8.10/lib/python3.8/site-packages/grafanalib/_gen.py", line 223, in generate_dashboard
    dashboard = loader(opts.dashboard)
  File "/Users/jwalgran/.pyenv/versions/3.8.10/lib/python3.8/site-packages/grafanalib/_gen.py", line 60, in loader
    spec.loader.exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 848, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/Users/jwalgran/Downloads/bargauge_auto_example.dashboard.py", line 6, in <module>
    BarGauge(orientation="auto"),
  File "<attrs generated init grafanalib.core.BarGauge>", line 76, in __init__
  File "/Users/jwalgran/.pyenv/versions/3.8.10/lib/python3.8/site-packages/attr/validators.py", line 307, in __call__
    raise ValueError(
ValueError: ("'orientation' must be in ['horizontal', 'vertical'] (got 'auto')", Attribute(name='orientation', default='horizontal', validator=<in_ validator with options ['horizontal', 'vertical']>, repr=True, eq=True, eq_key=None, order=True, order_key=None, hash=None, init=True, metadata=mappingproxy({}), type=None, converter=None, kw_only=False, inherited=False, on_setattr=None, alias='orientation'), ['horizontal', 'vertical'], 'auto')

How to reproduce it?

Create bargauge_auto_example.dashboard.py

from grafanalib.core import *

dashboard = Dashboard(
    panels=[
        BarGauge(orientation="auto"),
    ],
    title="Operations Dashboard",
).auto_panel_ids()

Attempt to generate JSON

 generate-dashboard bargauge_auto_example.dashboard.py > bargauge_auto_example.dashboard.json

Additional context

Definition of the BarGauge.orientation attribute is here

https://github.com/weaveworks/grafanalib/blob/c82a6794b5cdd19acbd60de3a7465226f40c4a7e/grafanalib/core.py#L3372-L3375

The documentation for BarGauge list auto as a valid option

https://grafana.com/docs/grafana/latest/panels-visualizations/visualizations/bar-gauge/#orientation