Add pipeline to trigger release process

Add a new multi-branch pipeline to check the JIRA release date of a version, and trigger the release if it is due in 3 working days, by notifying on #hotfix-releases Slack channel.

Existing pipeline for 10.10: https://qa2.nuxeo.org/jenkins/job/Private/job/Support/job/Hotfix_release_check/

Before triggering the release process, this pipeline must check that all blocker issues are marked as resolved for 2021.x or 2021.NEXT_HF_NUMBER in JIRA and their related commits are in the latest build tag candidate for promotion (2021.NEXT_HF_NUMBER.Y). If it is not the case, the build must fail and notify it in #hotfix-releases. It will be re-triggered the following day.