Update documentation and add pipeline steps
This MR adds the following jobs in the pipeline:
- Lint for YAML
- Rubocop through GitLab styles gem (same used in the monolith) -- Allow failure has been set to true to be fixed in follow up MRs.
- License scanning (only when Gemfile.lock changes)
- Dependency scanning (only when Gemfile.lock changes)
This MR also updates README.md and DEVELOPMENT.md based on the most recent changes
Related issue: gitlab-org/gitlab#322653 (closed)
Edited by Zamir Martins