Update notebooks with new EDA methods

[alex-hse-repository]

🚀 Feature Request

Update notebooks with new EDA methods

Motivation

Make users familiar with the new method

Proposal

1. Backtest

• Use another model, Prophet generates tones of logs
• Show logic with FoldMask
• Add example for metric_per_fold_distribution_plot, plot_metric_per_segmnet, plot_residuals, prediction_error_plot

2. Outliers

• Try to use SARIMAX instead of Prophet
• Improve phrase with "sequence outliers", we don't have method for them anymore
• Add examples for plot_imputation

3. Ensembles

• Add note about the new weighting strategy "auto" in VotingEnsemble

4. EDA

• Add examples for plot_time_series_with_change_points, plot_trend, stl_plot, seasonal_plot, plot_periodogram

Test cases

No response

Alternatives

No response

Additional context

No response

Checklist

• [ ] I discussed this issue with ETNA Team