Backtest using specified feature job setting.
>>> analysis = fb.FeatureJobSettingAnalysis.get_by_id(<analysis_id>)
>>> # Backtest a manual setting
>>> manual_setting = fb.FeatureJobSetting(
... blind_spot="135s",
... period="60m",
... offset="90s",
... )
>>> backtest_result = analysis.backtest(feature_job_setting=manual_setting)