Add SonarCloud support

[raits]

Added support for running SonarQube tests in the SonarCloud environment, which required defining the related properties inside gradle.properties instead of build.gradle. This allows us to override them via the command line. The defaults were left to our internal SonarQube so that Jenkins pipelines would continue to work for now.

Also introduced scanning with SonarCloud to the X-Road testing workflow on GitHub.

[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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