Added support for the Stylelint JSON report format

[ugrave]

Add support for built-in json format of stylelint reports. Skips the requirement of an additional npm package dependency.

Testing done

Manually testing has been done on a jenkins instance for both formats (json and checkstyle xml)

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[uhafner]

Thanks!