GitLab

This adds supports for Todos to link to Designs.

Add designs as a dropdown option

https://gitlab.com/gitlab-org/gitlab-ee/issues/13494
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15129

Co-Authored-By: Alex Kalderimis <akalderimis@gitlab.com>
Co-Authored-By: Luke Duncalfe <lduncalfe@eml.cc>