Add GitLab 17.3 and 17.4 and Mattermost 9.11 and 10.0 Changelog Entries

added Progress::2_ToDo label

assigned to @hueser93

mentioned in merge request !623 (merged)

added Progress::3_Doing label and removed Progress::2_ToDo label

mentioned in commit f0ebda39

closed with merge request !623 (merged)