Add target components logic into AutoRegressivePipeline

[alex-hse-repository]

🚀 Feature Request

Add target components logic into AutoRegressivePipeline

Proposal

In AutoRegressivePipeline

• Pass return_components flag into model's forecast
• Get target components from temporal dataset with get_target_components method after this line
  

  etna/etna/pipeline/autoregressive_pipeline.py

  Line 148 in ea1888e

  current_ts_future.inverse_transform(self.transforms)

• Return target components back into the final dataset using add_target_components after this line:

  etna/etna/pipeline/autoregressive_pipeline.py

  Line 156 in ea1888e

  prediction_ts.inverse_transform(self.transforms)

Test cases

• Check that when return_components=True dataset contain the correct target components for methods forecast, predict for dummy implementations

Additional context

Is blocked by #1167