Enable CI for TimeSquare

This enables a full CI/CD deployment using gitlab-ci

It is currently configured as follow:

• on simple push:
  • do a mvn clean verify, resulting artefact of the job contains a zip of the Eclipse update site
• on tag push, if the tag name is a release name (ie. /^\d+.\d+.\d+-?.*$/ for ex 1.0.0 or 1.0.0-rc1):
  • do a mvn clean verify
  • add the Eclipse update site in the package registry https://gitlab.inria.fr/jdeanton/TimeSquare/-/packages
  • create a release https://gitlab.inria.fr/jdeanton/TimeSquare/-/releases
  • publish the update site on https://timesquare.gitlabpages.inria.fr/updatesite/ (via a commit in https://gitlab.inria.fr/timesquare/timesquare.gitlabpages.inria.fr)
• on tag push, if the tag name is NOT a release name :
  • do a mvn clean verify
  • publish the update site on https://timesquare.gitlabpages.inria.fr/updatesite/ (via a commit in https://gitlab.inria.fr/timesquare/timesquare.gitlabpages.inria.fr)

Recommended release workflow:

• create a tag for the release using the recommended tag name, then push the tag
• force move tag latest to the same commit (in order to update https://timesquare.gitlabpages.inria.fr/updatesite/latest/index.html)
• adapt the text associated to the release (by default, it uses the latest commit message)