Add Danger's review roulette to CI

This MR adds https://gitlab.com/gitlab-org/ruby/gems/gitlab-dangerfiles to run Reviewer Roulette in CI which utilizes CI template added in gitlab-org/quality/pipeline-common!107 (merged).

Configuration on gitlab-styles

In order to make danger work properly I've create a new Project access token Danger bot with api scope and Maintainer role and added the CI/CD variable DANGER_GITLAB_API_TOKEN Masked but not Protected.

Project access token	CI/CD variable

Instructions extracted into gitlab-dangerfiles!84 (merged).

Screenshots

Seeing is believing