Add AutoRegressivePipeline to etna

[iKintosh]

🚀 Feature Request

Add AutoRegressivePipeline class that applies model in autoregressive style.

Motivation

According to Kaggle competitions there are numerous cases when applying regressor models in autoregressive style beats their classic kind.

Proposal

Add class AutoRegressivePipeline.
It should implement this interface:

AutoRegressivePipeline(model, transforms, horizon, step=1)

Where step show after how many steps features will be recalculated, also this value will be used as horizon parameter in TSDataset.make_future

Test cases

No response

Alternatives

No response

Additional context

No response

Checklist

• Added feature request
• Added motivation
• Added proposal