Remove duplicates from commit messages

[fjakop]

As developer we're using feature branches to implement story-based features. Typically we do interim commits just for sharing the code with our co-devs for the case of (un)expected absence (vacation, sicknes etc.).

At the moment, every commit has the same commit comment, e.g. "feat: new cool feature" and leads to as many changelog entries as there are commits, as we do use merge requests without squash.

The expected behaviour is that the commit messages would be deduped if they're completely identical.