Setup Sonar Quality Gate / Build Status

Setup a Sonar Quality Gate that prevents from quality decreasing.
Then, report the analysis result to the build status:

• Jenkins build unstable would be fine; failure is not wanted
• GitHub build status must fail if debt increases.

https://stackoverflow.com/questions/12513559/making-jenkins-build-unstable-when-sonar-limits-exceeded/12534077
https://blog.sonarsource.com/breaking-the-sonarqube-analysis-with-jenkins-pipelines/
https://wiki.jenkins.io/display/JENKINS/Quality+Gates+Plugin
https://docs.sonarqube.org/display/SONAR/Quality+Gates
https://github.com/SonarQubeCommunity/sonar-build-breaker
https://blog.sonarsource.com/why-you-shouldnt-use-build-breaker/
https://docs.sonarqube.org/display/SCAN/Analyzing+with+SonarQube+Scanner+for+Jenkins