[Cold Storage] New job to promote a build version as a release

Add a new simple pipeline running on the master branch with its related Jenkinsfile: release.groovy.
This job is parametrized with a Nuxeo build version (such as 2021.0.1) 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 v2021.0.1
  

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

  2021.0-SNAPSHOT -> 2021.0
  

• Add a release commit.

  git commit -m "Release v2021.0"
  

• Add a tag pointing to this release commit.

  git tag v2021.0
  

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

  2021.0-SNAPSHOT -> 2021.1-SNAPSHOT
  

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