Implement release process

Context

In the continuity of NEV-19, we now need to release the project.

NEV-19 brings preview environments on PRs, so we're able to have a stable reference branch and releasable at any moment.

Task

We need an extra validation in a NCO environment. This stage will take place before production deployment, so it will be outside of the repository scope.

See below the desired flow:

• nuxeo will trigger a job to start release process
• job will ask user if it's a feature/fix release (which allows NCO to do a lighter validation on fix release)
• job will release project with a RCX suffix
• job will notify NCO about this release
• (NCO will deploy the RC release)
• (NCO will notify QA to test the RC release)
• QA will notify jenkins if release is ok or not
  • release is ok: proceed to final release
  • release is not ok: work to fix it and then go back to job will release project with a RCX+1 suffix step