fix(Gradle): Correctly use specified version in build. Move version to gradle.properties. Upload correct artifact to release.

breaking(Addon Suite Upgrade): Move to new ServerPackCreator addon suite. Provide examples for all extension endpoints.  Examples for ConfigCheck-, ConfigPanel-, Tab-, PreGen-, PreZip- and PostGen extensions, global addon configuration, extension configuration and more.

breaking: Implement ServerPackCreator from GitLab Maven packages and provide basic example of a plugin

breaking: Remove start-script related code as this option is no longer available in ServerPackCreator

Initial commit. Provide base example of an addon for ServerPackCreator with documentation and tests.