improve reproducible build architecture for Spoon

[monperrus]

as part of the release pipeline, we should:

• automatically PR to https://github.com/jvm-repo-rebuild/reproducible-central/ (@hboutemy WDYT?)
• push the buildinfo file to Maven Central

[hboutemy]

no worries for Reproducible Central: I have automation that makes it easy to update without the help of projects
see https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/doc/add.md for details, if you are interested

at spoon level, what I really need is either no beta to Maven Central, or if you want to publich to Maven Central, publish a git tag as you do with releases: see https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/fr/inria/gforge/spoon/spoon-core/README.md

on rebuilding when something is published, I manage, no worry

[algomaster99]

publish a git tag as you do with releases

I have tried it here #5530. Just need a reviewer to look at it.