refactor: replace global metrics initialization

[chansuke]

Refactor global metric initialization.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 47.82609% with 12 lines in your changes missing coverage. Please review.

Project coverage is 63.34%. Comparing base (f6239f9) to head (16973e8).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/metrics/metrics.go	55.00%	6 Missing and 3 partials ⚠️
cmd/run.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1140      +/-   ##
==========================================
- Coverage   63.60%   63.34%   -0.27%     
==========================================
  Files          15       15              
  Lines        2341     2357      +16     
==========================================
+ Hits         1489     1493       +4     
- Misses        760      769       +9     
- Partials       92       95       +3     

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[chengfang]

@chansuke thanks for the contribution. Can you add description to this PR, including the rational for the change, etc?

Also can you fix the DCO check failure?