WIP: menus: add a version-specific issues link to the GIMP gitLab issues

The idea is that this may make it easier for users to spot whether an issue the have encountered is already known, like the infamous export crash in 2.99.4. That's also why the link being used shows all reports: open and closed ones.

The current state would work fine for releases, provided that issues have a correspnding version label. For this reason, we should make sure that version labels are not replaced, but added to, unless a specific issues is indeed not present in an intermediate release inbetween some others.

The naive approach of simply using (gimp-version) for the label fails for development versions in between releases, as e.g. we have no issues with a '2.99.5' label.