parent-pom: add <distributionManagement> for deployments on GitHub
parent-pom: add <distributionManagement> for deployments on GitHub

This uses the Kurento/kurento-java GitHub registry to publish packages
by default when `mvn deploy` is used.

Kurento/kurento-java,Kurento/kurento-java,Kurento/kurento-java,Kurento/kurento-java