Attempt to fix bug with exogs in AutoRegressivePipeline

[Mr-Geekman]

IMPORTANT: Please do not create a Pull Request without creating an issue first.

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?

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

1. Create current_ts in AutoRegressivePipeline._forecast with exogs.
2. Recreate prediction forecast from scratch with exogs at the end of AutoRegressivePipeline._forecast.

Related Issue

#570.

Closing issues

Closes #570.

[github-actions]

🚀 Deployed on https://deploy-preview-647--etna-docs.netlify.app

[codecov-commenter]

Codecov Report

Merging #647 (8298044) into master (6c52e29) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #647   +/-   ##
=======================================
  Coverage   84.33%   84.33%           
=======================================
  Files         118      118           
  Lines        6268     6270    +2     
=======================================
+ Hits         5286     5288    +2     
  Misses        982      982           

Impacted Files	Coverage Δ
etna/pipeline/autoregressive_pipeline.py	95.83% <100.00%> (+0.18%)	⬆️

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[martins0n]

👍