Mattermost 3.5 config update
Followup to https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1104 to add the new config options
Includes the commits from the parent merge request, so it should go in first.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Followup to https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1104 to add the new config options
Includes the commits from the parent merge request, so it should go in first.