Add experimental classification

[alex-hse-repository]

Before submitting (must do checklist)

• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
• Did you update the CHANGELOG?

Proposed Changes

Closing issues

[github-actions]

🚀 Deployed on https://deploy-preview-985--etna-docs.netlify.app

[codecov-commenter]

Codecov Report

Merging #985 (2a5050d) into master (124353a) will increase coverage by 0.37%.
The diff coverage is 97.91%.

@@            Coverage Diff             @@
##           master     #985      +/-   ##
==========================================
+ Coverage   84.87%   85.25%   +0.37%     
==========================================
  Files         148      157       +9     
  Lines        8020     8258     +238     
==========================================
+ Hits         6807     7040     +233     
- Misses       1213     1218       +5     

Impacted Files	Coverage Δ
...rimental/classification/feature_extraction/base.py	87.50% <87.50%> (ø)
...mental/classification/feature_extraction/weasel.py	97.67% <97.67%> (ø)
etna/experimental/classification/classification.py	98.24% <98.24%> (ø)
etna/experimental/classification/__init__.py	100.00% <100.00%> (ø)
etna/experimental/classification/base.py	100.00% <100.00%> (ø)
...ntal/classification/feature_extraction/__init__.py	100.00% <100.00%> (ø)
...ental/classification/feature_extraction/tsfresh.py	100.00% <100.00%> (ø)
etna/experimental/classification/predictability.py	100.00% <100.00%> (ø)
etna/experimental/classification/utils.py	100.00% <100.00%> (ø)
etna/settings.py	73.88% <100.00%> (+1.22%)	⬆️
... and 1 more

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[martins0n]

We should add comment to changelog

[martins0n]

chanelog