Multi project pipeline

We have types two pipelines:

1. Delivery pipeline: multiple stages, one project, similar to naming in Jenkins, planning to build 8.8
2. Dependency pipeline: projects, like https://ci.concourse.ci/

In addition to triggers in .gitlab-ci.yml and the API we also need dependencies that you define in .gitlab-ci.yml per project. All multi project visualizations can be based on this, you need read access to the other projects You don't have one uber pipeline defined somewhere, projects depend on each other to define the pipeline together.

Maybe have a new name for delivery pipeline to prevent confusion, but it makes sense to follow Jenkins terminology. We can show the dependency pipeline even in the project view, there is no group view needed for this.

We'll first deliver the delivery pipeline.