Add CI report types section to development guides
Summary
Development Guides - https://docs.gitlab.com/ee/development/
We should add a CI report types section to the development guides. It should cover the CI report types architecture and the things that need to get done to implement new report types. This is a relatively common addition (adding new report types) that's non-trivial and has several moving parts - having this documented could possibly speed up development by removing the need for engineering discovery needed to add a new report type.
This idea came when I listed all of the things needed to implement a new report type as part of https://gitlab.com/gitlab-org/gitlab-ee/issues/9788#note_155760761 so I could track the development of that feature.