Publish the source JARs

[pcdavid]

Unless I'm missing something, we do not publish the source JARs as part of the deployment to GitHub Packages:

• https://github.com/ObeoNetwork/Flow-Designer/packages/382766 does not show the -sources JAR.
• locally, my m2e install, which is normally configured to fetch sources of dependencies, does not seem to find them.

I have not tested them, but see:

• https://maven.apache.org/plugins/maven-deploy-plugin/examples/deploying-sources-javadoc.html
• https://stackoverflow.com/questions/4725668/how-to-deploy-snapshot-with-sources-and-javadoc