ci: add review roulette danger plugin

Description

This MR enables danger on this project and "reviewer roulette".

See

• Danger's comment
• danger-review job
• https://gitlab.com/gitlab-org/ruby/gems/gitlab-dangerfiles/#simple_roulette
• https://gitlab.com/gitlab-org/ruby/gems/gitlab-dangerfiles/#without-gemfile
• https://about.gitlab.com/handbook/engineering/projects/#gitlab-cli
• https://gitlab-org.gitlab.io/gitlab-roulette/?currentProject=gitlab-cli&sortKey=stats.avg30&mode=hide&order=-1&hourFormat24=true

Related Issues

Related to ci: add danger-review job (#1103 - closed)

How has this been tested?

Screenshots (if appropriate):

Danger comment in this very MR 👇

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)