Replace the GHA by an updatecli manifest

[lemeurherve]

So we're sure the docker image is published before opening a pull request (cf https://github.com/jenkins-infra/docker-jenkins-lts/pull/379)

[dduportal]

Side benefits:

• No more "weird" mix of PRs embeding both plugins and core versions
• Reconsidering the curent triggers (either github action or moving to Jenkins pipeline):
  • Should run on (EU) night between wednesday and thursdays (after LTS usual day)
  • Allow to trigger a brun manually

[lemeurherve]

Note for self: do the same for https://github.com/jenkins-infra/docker-jenkins-weekly