Enable Checkstyle fail on violation

A few things to consider:

1. We currently override Checkstyle rules defined in kie-parent. The intention was likely to make the rules more strict, i.e. kie-parent rules should be a subset of optaplanner rules but that's not guaranteed since we override the configuration instead of merging it. It would be nice to have a way to merge the configurations to avoid getting out of sync with kie-parent.
2. The Checkstyle rules are just basic checks. Can we extend them to cover most of the KIE Java Conventions? When adding new rules, always keep reasonable build time a top priority. You can use https://github.com/jcgay/maven-profiler to measure Checkstyle plugin execution time.