Provide task group variable for Mylyn commit comment template

[esocode]

It would be nice to have a variable in the Mylyn commit comment template like ${task.group} that provides access to the Gitlab group of an issue. Or alternatively ${task.url} which is always empty currently could contain the complete relative URL of an issue's project (e.g. group/[subgroup/...]project. Without the full path Gitlab cannot match commits that are done in multiple projects under the issue of a particular project. The only workaround is to edit the commit message by hand on each commit.