Add distribution classes for AutoML

[Mr-Geekman]

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

Look #1290.

Closing issues

Closes #1290.

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Codecov Report

Merging #1292 (e826165) into automl-2.0 (ec40caf) will increase coverage by 0.29%.
The diff coverage is 99.48%.

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@@              Coverage Diff               @@
##           automl-2.0    #1292      +/-   ##
==============================================
+ Coverage       88.26%   88.56%   +0.29%     
==============================================
  Files             187      189       +2     
  Lines           11480    11436      -44     
==============================================
- Hits            10133    10128       -5     
+ Misses           1347     1308      -39     

Impacted Files	Coverage Δ
etna/distributions/distributions.py	96.00% <96.00%> (ø)
etna/auto/auto.py	95.71% <100.00%> (-0.15%)	⬇️
etna/auto/utils.py	85.71% <100.00%> (+12.03%)	⬆️
etna/distributions/__init__.py	100.00% <100.00%> (ø)
etna/ensembles/direct_ensemble.py	96.72% <100.00%> (-0.11%)	⬇️
etna/ensembles/stacking_ensemble.py	98.26% <100.00%> (-0.03%)	⬇️
etna/ensembles/voting_ensemble.py	95.60% <100.00%> (-0.10%)	⬇️
etna/models/base.py	86.77% <100.00%> (-0.07%)	⬇️
etna/models/catboost.py	100.00% <100.00%> (ø)
etna/models/deadline_ma.py	98.71% <100.00%> (-0.02%)	⬇️
... and 33 more

... and 2 files with indirect coverage changes

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🚀 Deployed on https://deploy-preview-1292--etna-docs.netlify.app

[Mr-Geekman]

We should discuss how we are going to make documentation for etna.distributions is we are going to keep it that way.