feat: add server alias for serve command

[snitin315]

What kind of change does this PR introduce?
Feature

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

Summary

Add server alias for serve command.

Usage - webpack serve|server|s [entries...] [options]

Does this PR introduce a breaking change?
No

Other information
No

[codecov]

Codecov Report

Merging #2631 (0ce5416) into master (e72e17d) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2631      +/-   ##
==========================================
+ Coverage   95.23%   95.30%   +0.06%     
==========================================
  Files          31       31              
  Lines        1512     1512              
  Branches      429      429              
==========================================
+ Hits         1440     1441       +1     
+ Misses         72       71       -1     

Impacted Files	Coverage Δ
packages/serve/src/index.ts	91.22% <ø> (ø)
packages/webpack-cli/lib/webpack-cli.js	96.14% <ø> (ø)
packages/generators/src/addon-generator.ts	95.45% <0.00%> (+2.27%)	⬆️

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[alexander-akait]

Thanks