Add a link to GitLab issue to a corresponding MDMS document container

It would be cool to link MDMS documents back to GitLab issues.

We could add a comment to a document with the gitlab link.

Not sure how complicated it is. Probably we will need to keep track of the session, cookies PHPSESSID etc. We will also need to parse the existing comment section to make sure that the script does not add duplicate entries.

Some basic ideas on how to do it are inside feature_comments branch.