feat: add testing-utilities package

[juanpicado]

Type: feat
Scope: testing-utilities

Description:

Add a new package named @verdaccio/testing-utilities, which is intended to add multiple methods for testing across all plugins and also UI. Generate metadata easily to avoid boilerplate.

[codecov]

Codecov Report

Merging #214 into master will increase coverage by 0.05%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master     #214      +/-   ##
==========================================
+ Coverage   65.25%   65.31%   +0.05%     
==========================================
  Files          25       26       +1     
  Lines        1390     1401      +11     
  Branches      201      204       +3     
==========================================
+ Hits          907      915       +8     
- Misses        481      483       +2     
- Partials        2        3       +1

Flag	Coverage Δ
#core	88.18% <ø> (ø)	⬆️
#plugins	58.35% <ø> (-0.08%)	⬇️

Impacted Files	Coverage Δ
tools/testing-utilities/src/package-generator.ts	90.9% <90.9%> (ø)
plugins/local-storage/src/local-fs.ts	86.58% <0%> (-1.22%)	⬇️
plugins/memory/src/memory-handler.ts	87.17% <0%> (ø)	⬆️

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