Jupyter Notebook with exogenous data examples

[iKintosh]

🚀 Feature Request

Add Jupyter Notebook with examples on how to use exogenous data

Motivation

It would be nice to have examples for exogenous data and how easy to use it with etna.

Proposal

1. Find open dataset with exogenous data (covid for example)
2. Describe how additional data and regressors are different (both exogenous data)
3. Show how to make additional data into regressor and why it is necessary
   • Show what to do if exogenous series is common for all series
   • Show what to do if each series has its own exogenous series
4. Show that models work with exogenous data automatically

Test cases

No response

Alternatives

No response

Additional context

No response

Checklist

• I discussed this issue with ETNA Team

[julia-shenshina]

is blocked by all the issues from Regressors 2.0 milestone

[alex-hse-repository]

We can use dataset from this competition with weather dataset as exogenous data