Project name isn't rendered in Mattermost pipeline notifications

Summary

We recently overhauled the look of pipeline chat notifications in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27683. There are a couple of features that the new notifications rely on that are not yet supported by Mattermost, specifically:

1. Footers, which display the project name and pipeline timestamp
2. “good”, “warning”, and “danger” values in the color parameter, which indicate the pipeline's status

#1 is most important, since the project name was previously included in the notification's text; Mattermost users no longer can tell what project the notification is from just by glancing at the notification.

More info: https://docs.mattermost.com/developer/message-attachments.html?highlight=footer#known-issues

This issue was identified in this comment: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27683#note_208012212

Update

It appears that Mattermost does support “good”, “warning”, and “danger” color values, despite what their documentation says.