feat: implement new configtest command

[snitin315]

What kind of change does this PR introduce?
feature

Did you add tests for your changes?
WIP
If relevant, did you update the documentation?
WIP
Summary

Syntax - webpack configtest <path-to-config>

Does this PR introduce a breaking change?
No

Other information
Fixes #803

[snitin315]

Should we support validating multiple configs simultaneously like webpack configtest <first-config> <second-config>? or throw error can't validate multiple configs simultaneously. please provide one config at a time. and exit.

Need to discuss /cc @webpack/cli-team

[snitin315]

I think it might be not possible for multiple configs as the process will exit as soon as an error config is found.

[alexander-akait]

Also please add this package to webpack-cli package.json (in peerDependenciesMeta) too

[alexander-akait]

Good job

[alexander-akait]

Feel free to covert it to completed PR from Draft, I think we can merge it

[snitin315]

Let's see how CI run goes.

[snitin315]

Ah, need some tweaks for webpack-4

[codecov]

Codecov Report

Merging #2303 (1ceb0cb) into master (4ea0cb4) will increase coverage by 19.11%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #2303       +/-   ##
===========================================
+ Coverage   67.81%   86.93%   +19.11%     
===========================================
  Files          63       15       -48     
  Lines        2486      995     -1491     
  Branches      572      284      -288     
===========================================
- Hits         1686      865      -821     
+ Misses        800      130      -670     

Impacted Files	Coverage Δ
packages/webpack-cli/lib/webpack-cli.js	89.69% <ø> (+0.10%)	⬆️
packages/webpack-cli/lib/index.js	87.50% <0.00%> (-12.50%)	⬇️
packages/generators/src/loader-generator.ts
packages/generators/src/types/index.ts
packages/migrate/src/index.ts
packages/generators/src/utils/index.ts
packages/generators/src/utils/helpers.ts
packages/generators/src/utils/plugins.ts
packages/generators/src/utils/tooltip.ts
packages/utils/src/global-packages-path.ts
... and 41 more

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[alexander-akait]

/cc @webpack/cli-team need review

[alexander-akait]

Need small improve

[rishabh3112]

Looks good, left few suggestions.

[webpack-bot]

@snitin315 Thanks for your update.

I labeled the Pull Request so reviewers will review it again.

@alexander-akait Please review the new changes.