Document using jenkinsfile-runner for Jenkins migration
Problem to solve
Migrating to Jenkins can be complicated, as discussed at #22165 (comment 245126542) there is a Jenkinsfile runner (https://github.com/jenkinsci/jenkinsfile-runner) that we could call from normal GitLab CI, making first steps of migration very easy. @ctimberlake1 wrote a version of how this could work at https://lackastack.net/posts/gitlabci-jenkinsfile/ that could be adapted.
As part of our Jenkins Wrapper MVP(#208277 (closed)) we are building a CLI tool (#208848 (closed)) to automate as much of the process as possible for extracting a users Jenkins server configuration for running in GitLab Runners. However, a significant portion of this process will involve manual steps.
We should document the usage of the tooling, along with updated content from https://lackastack.net/posts/gitlabci-jenkinsfile/, in the README for the tooling. We will not update the official documentation in order to avoid providing the sense of any warranty or fitness at this point, but the README will contain everything you need to use it.
Relevant to CS/Sales teams