Wape metric

[looopka]

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

Add new metric WAPE. reference https://www.baeldung.com/cs/mape-vs-wape-vs-wmape

Closing issues

closes #1080

[codecov-commenter]

Codecov Report

Merging #1085 (aa44851) into master (30f9277) will decrease coverage by 18.63%.
The diff coverage is 66.66%.

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@@             Coverage Diff             @@
##           master    #1085       +/-   ##
===========================================
- Coverage   87.06%   68.44%   -18.63%     
===========================================
  Files         170      170               
  Lines        9310     9319        +9     
===========================================
- Hits         8106     6378     -1728     
- Misses       1204     2941     +1737     

Impacted Files	Coverage Δ
etna/metrics/functional_metrics.py	44.11% <20.00%> (-42.09%)	⬇️
etna/metrics/metrics.py	86.25% <87.50%> (-13.75%)	⬇️
etna/metrics/__init__.py	100.00% <100.00%> (ø)
etna/commands/__main__.py	0.00% <0.00%> (-87.50%)	⬇️
etna/datasets/hierarchical_structure.py	22.01% <0.00%> (-75.23%)	⬇️
etna/libs/pmdarima_utils/arima.py	28.84% <0.00%> (-71.16%)	⬇️
etna/pipeline/assembling_pipelines.py	26.31% <0.00%> (-71.06%)	⬇️
etna/pipeline/mixins.py	31.42% <0.00%> (-67.62%)	⬇️
etna/analysis/outliers/hist_outliers.py	10.82% <0.00%> (-66.25%)	⬇️
etna/reconciliation/bottom_up.py	35.29% <0.00%> (-64.71%)	⬇️
... and 62 more

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