feature request: running pipelines locally

Hello from kubernetes/test-infra! :wave: -- We think the pipeline is really interesting and we'd like to use it more, and we (I) have a feature request which we get a lot with our current "jobs" system:

how do I test this [job definition] on my machine

and

how do I run this test job [to test code for some repo using the jobs for ci]

We've considered solving this for "ProwJobs" and while looking at prior art I found https://github.com/GoogleCloudPlatform/cloud-build-local, which has an implementation of this for GCB which looks a bit similar ...

I'd like to start a discussion around how we could potentially accomplish this for the build pipeline.

For the first case just being able to run it locally in some form is sufficient, for the second case users would likely want to be able to mount not-yet-pushed code to the job and build / test that.

If you all are interested, I'd like to help with this.

I think it could be a "killer" feature to be able to iterate on running and testing your containerized pipelines locally before submitting them to whatever CI you will use in production. I know Prow users would love this.

cc @bobcatfish