Enhance HolidayTransform

[malodetz]

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

See #763

Closing issues

Closes #763

[codecov-commenter]

Codecov Report

Merging #1340 (3dfac4b) into master (f4bcc29) will decrease coverage by 0.17%.
The diff coverage is 93.33%.

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@@            Coverage Diff             @@
##           master    #1340      +/-   ##
==========================================
- Coverage   89.15%   88.99%   -0.17%     
==========================================
  Files         204      204              
  Lines       12675    12681       +6     
==========================================
- Hits        11300    11285      -15     
- Misses       1375     1396      +21     

Files Changed	Coverage Δ
etna/transforms/timestamp/holiday.py	97.82% <93.33%> (-2.18%)	⬇️

... and 9 files with indirect coverage changes

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[github-actions]

🚀 Deployed on https://deploy-preview-1340--etna-docs.netlify.app

[Mr-Geekman]

Very good. There are very small changes requested.