Add 'merged' label when merging with squash-commits

Currently, after merging a branch to the default branch, Gitlab adds the tag 'merged' to the source branch. This gives a clear overview of which branches still need some updates and merging and which branches are completed. It also allows users to efficiently clean up branches by using the delete merged branches option.

However, when merging using squash-commits, this label does not get added to the source branch.

This is most likely due to the fact that squash creates and merges with a new branch. So as a solution either:

• Add a tag 'merged' to the source branch
• Add a tag 'squash-merged' to the source branch