[TASK] Release version 1.6.0

Upload version 1.6.0 to TER.

Resolves: #58583
Releases: 1.6
Change-Id: I9eb78f45a8b685a712e27c7c928bcab1f13ead71
Reviewed-on: https://review.typo3.org/29988
Reviewed-by: Francois Suter
Tested-by: Francois Suter