Admin message

As a result of the planned maintenance of the TU Delft RID data center from December 10 till 17, GitLab will be mostly unavailable during that full week. While we are trying to minimize impact (e.g. by trying to shorten the time frame and seeing if parts can remain running in read-only mode), there is simply not enough storage available in our second data center to move our git repositories. Prepare for this interruption now and inform others where needed. We will update this banner if we get more details; further information (especially if/once GitLab is down) on our Mattermost channel: https://mattermost.tudelft.nl/educational-software-support/channels/gitlab