This is the build-helper-maven-plugin contains serveral goals to support you in different kinds of task, like parsing version information, add supplemental source/test folders to a Maven project or attach supplemental artifacts.
More details can be found on the goals overview page.
gpg-agent is running.mvn -B release:prepare release:performFor publishing the site do the following:
cd target/checkout
mvn verify site site:stage scm-publish:publish-scm