myjenkins: Integrate the Jenkins Warnings Next Generation Plugin

[gmacario]

See https://github.com/jenkinsci/warnings-ng-plugin

For more details please refer to the documentation or to an introductory video.

[gmacario]

Testing on http://nemo.gmacario.it:9080/ (commit b881b15)

Login as gpmacario@nemo

cd ~/github/gmacario/easy-jenkins/
git pull --all --prune
docker-compose pull
docker-compose build --pull
./runme.sh

Browse ${JENKINS_URL}

• Login as user admin

Click ${JENKINS_URL} > Manage Jenkins > Manage Plugins > Available

• Filter by "warning-ng"
• Check "Warnings Next Generation"
• Click "Download now and install after restart"