S3 and file logger -- change experiment folder name timestamp rounding

[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 #947

Closing issues

Closes #947

[codecov-commenter]

Codecov Report

Merging #1264 (b79d60a) into master (d224aec) will increase coverage by 0.35%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master    #1264      +/-   ##
==========================================
+ Coverage   87.63%   87.98%   +0.35%     
==========================================
  Files         175      186      +11     
  Lines       10438    10751     +313     
==========================================
+ Hits         9147     9459     +312     
- Misses       1291     1292       +1     

Impacted Files	Coverage Δ
etna/loggers/file_logger.py	73.21% <100.00%> (ø)

... and 13 files with indirect coverage changes

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[github-actions]

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[alex-hse-repository]

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