When using jenkinsfile-runner inside Kubernetes such as with Prow/Knative Build in Jenkins X it would be awesome to be able to replicate the kubernetes-plugin style execution of commands in sidecars all from within the exact same pod. e.g.

sh "echo this runs in the same container as the jenkinsfile runner"
container("selenium") {
   sh "echo this runs in the selenium container"
} 

When using pure knative build steps this stuff all works already; but its not yet supported in a Jenkinsfile.

I understand that the jenkinsfile runner is just 1 container that runs & isn't gonna be able to grok the sidecar containers - but thats fine - we can configure that stuff outside of the jenkisnfile + jenksinfile-runner - but it'd be nice to be able to execute commands in sidecar containers (e.g. via the shell command:

kubectl exec -it $HOSTNAME -c selenium -- echo "this runs in the selenium continaer"