Add ConfidenceIntervalOutliersTransform

[alex-hse-repository]

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• 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?

Type of Change

• Examples / docs / tutorials / contributors update
• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Proposed Changes

Add ConfidenceIntervalOutliersTransform

Related Issue

Closing issues

[julia-shenshina]

Looks great!
Could you please update outliers example notebook with ci method?

[codecov-commenter]

Codecov Report

Merging #196 (4550773) into master (76d95ae) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #196      +/-   ##
==========================================
+ Coverage   88.01%   88.07%   +0.06%     
==========================================
  Files          76       76              
  Lines        3505     3523      +18     
==========================================
+ Hits         3085     3103      +18     
  Misses        420      420              

Impacted Files	Coverage Δ
etna/transforms/__init__.py	100.00% <100.00%> (ø)
etna/transforms/outliers.py	98.83% <100.00%> (+0.22%)	⬆️
etna/transforms/sklearn.py	95.83% <0.00%> (+0.18%)	⬆️

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