Add code review guidelines related to Build [CI skip].
What does this MR do?
Add specific code review guidelines, moved from handbook to gitlab docs as recommended by @rymai in https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/6936
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Add specific code review guidelines, moved from handbook to gitlab docs as recommended by @rymai in https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/6936