Add name property to Metric class

[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

Look #446

Related Issue

#446

Closing issues

Closes #446

[codecov-commenter]

Codecov Report

Merging #454 (1fe9914) into master (4659990) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #454   +/-   ##
=======================================
  Coverage   87.79%   87.80%           
=======================================
  Files         114      114           
  Lines        5351     5354    +3     
=======================================
+ Hits         4698     4701    +3     
  Misses        653      653           

Impacted Files	Coverage Δ
etna/metrics/base.py	96.61% <100.00%> (+0.18%)	⬆️
etna/pipeline/pipeline.py	97.39% <100.00%> (ø)

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