Release build process

1. Run mvn clean install to build the plugin repository at releng/io.openliberty.tools.update/target/repository
2. Sign the jar files located in features and plugins (no need to sign the content.jar or artifact.jar)
3. Replace the unsigned jars with the signed jars in the same "repository" directory
4. Run the following command to update the "checksum" values in the artifact.xml with the new checksum values of the signed jars:

mvn -pl releng tycho-p2-repository:fix-artifacts-metadata