Fix react development server and add GitHub action for dynamic workflows.

[mshima]

• Fixes react development server
  • Update npm scripts
  • Update webpack config
  • Disable source-map to workaround Warning when compiling with React #16116
• Add build-matrix action to allow dynamic workflows for modularized tests
• Add trailing -- to composite npm scripts.
  • Allows scripts to call others scripts passing escaped parameters (-- --arg) correctly.
    Without needing double escaping -- -- --arg
• Add Dev Server workflow for testing webpack-devserver, browser sync and dev profile.

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• All continuous integration tests are green
• Tests are added where necessary
• The JDL part is updated if necessary
• jhipster-online is updated if necessary
• Documentation is added/updated where necessary
• Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

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[Tcharl]

Reviewed, looks OK

[mshima]

Approved merging.

[deepu105]

@mshima I have assigned a bounty for this, please claim the same

[mshima]

@pascalgrimaud bounty claimed https://opencollective.com/generator-jhipster/expenses/52030

[pascalgrimaud]

@mshima : approved