Test and document the steps to use CI/CD for external repo for security checks

Now that we have CI/CD for external repo we need to document how to leverage this feature to have "security pipelines" for GitHub projects. This can be a good driver for interested customers that want to use GitLab for security checks.

We could consider different scenarios:

  1. GitHub.com repo and GitLab.com CI/CD
  2. GitHub Enterprise and GitLab.com CI/CD
  3. GitHub Enterprise and GitLab Enterprise
  4. GitHub.com and GitLab Enterprise

I suppose the most important cases are 1 and 2, so we can focus on them first.

For each case, we should test and document how to set up the project, and which are the expected results. This could be done as a technical article (https://docs.gitlab.com/ce/development/writing_documentation.html#technical-articles).

Example TOC:

  1. Setup
  2. create a CI/CD project for external repo on GitLab
  3. connect your GitHub.com account using OAuth2
  4. select one of the projects hosted on GitHub
  5. (optional) schedule a pipeline to run checks automatically every hour
  6. push a .gitlab-ci.yml with the security pipeline definition to the original GitHub project
  7. Usage
  8. push changes to the original project on GitHub
  9. wait for the status no GitHub to update
  10. click the link to go to the GitLab pipeline
  11. select the security tab to see the report