Use new Maven Plugin to Handle CoreMedia Plugins

CoreMedia plugins are now synchronized by means of the coremedia-plugins-maven-plugin which handles adding, removing and downloading the respective plugins. The Groovy scripts in the <workspace>-app/pom.xml files (e.g. cae/spring-boot/cae-live-app/pom.xml) have been replaced with the coremedia-plugins-maven-plugin which supports caching of downloaded artifacts and respects Maven's proxy settings.

(CMS-20775)