Add a roulette.json file to about.gitlab.com

Required for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24938

We need to load certain data from team.yml for each CI pipeline, to recommend reviewers and maintainers to the author.

This MR adds a roulette.json file, modelled after team.json, containing just the data we need.

I didn't want to add the additional data to team.json, since that would mean people began loading additional unnecessary information elsewhere. Having a single, dedicated endpoint also means it's less likely the data will be changed in incompatible ways.