Add function to duplicate exogenous data

[iKintosh]

🚀 Feature Request

Add functions to utils to duplicate exogenous data by the number of segments

Motivation

Sometimes we have same exogenous data for all segments. In order to use it with etna it should be duplicated for all segments. We should have some utils to do it with ease.

Proposal

Expect data in the format of

data	value
01-01-2021	12

exod_single: pd.DataFrame
list_of_segments: List[str]

result_df = duplicate_data(df=exod_single, segments=list_of_segments, format: str = "long")

the result should be

data	value	segment
01-01-2021	12	segment_1

Function should

• duplicate exogenous data by the number of given segments
• add proper segment names to columns
• should have option flag on how to return data:
  • wide format (TSDataset format)
  • long format (old format)

Test cases

• Duplicates data
• Keeps selected format

Alternatives

No response

Additional context

No response

Checklist

• I discussed this issue with ETNA Team