Expose GitLab version as a CI/CD variable
Description
With the ability to include external resources as part of the pipeline definition (https://gitlab.com/gitlab-org/gitlab-ce/issues/20868), users have less control over their .gitlab-ci.yml
file.
If some of the included files rely on a feature that changed at some point with a specific release, the change to adapt must be done in all the files that include it. If we export the GitLab version as a CI/CD variable, the "source" script/template can handle it properly, and it will be transparent to all the projects that include it.
Proposal
Expose a new CI/CD variable named GITLAB_VERSION
that contains the version number of GitLab.