[CI] New job to promote a build version as a release

Add a new simple pipeline running on the master branch with its related Jenkinsfile: promote.groovy.
This job is parametrized with a Nuxeo build version (such as 3.0.0-rc.0) to promote a given build as a release.
For now, it's triggered manually.

This job should:

• Checkout the build tag to promote.

  git checkout v3.0.0-rc.0
  

• Update the new Maven POM with the released version by removing -SNAPSHOT.

  3.0.0-SNAPSHOT -> 3.0.0
  

• Add a release commit.

  git commit -m "Release 3.0.0"
  

• Add a tag pointing to this release commit.

  git tag v3.0.0
  

• Update the master branch version to the next SNAPSHOT version. Also, update the new Maven POM.

  3.0.0-SNAPSHOT -> 3.0.1-SNAPSHOT
  

• Validate the updated POMs and push to GitHub.
• Upload Nuxeo Aspera Connector Package to Connect prod.