Add Success Policy to JobSet API

[danielvegamyhre]

Fixes #82
Fixes #120

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[kannon92]

/lgtm
But probably should leave final approval for @ahg-g.

[ahg-g]

/hold

just in case it merges by mistake

[kannon92]

/hold

just in case it merges by mistake

Sorry about that. Forgot that /lgtm will cause a merge since you and @danielvegamyhre are approvers.

[ahg-g]

/label tide/merge-method-squash
/hold cancel
/lgtm

[vsoch]

Did some testing! For others interested in doing this, you need to install the development version to your cluster and the module from the main branch reference:

# For your cluster
kubectl apply --server-side -k github.com/kubernetes-sigs/jobset/config/default?ref=main

# For your operator (if relevant)
go get sigs.k8s.io/jobset@main

And then testing - I tested a job name that didn't exist, this seems like the correct result!

2023-05-19T23:57:34Z    DEBUG   controller-runtime.webhook.webhooks     wrote response  {"webhook": "/validate-jobset-x-k8s-io-v1alpha1-jobset", "code": 403, "reason": "invalid replicatedJob name 'broker' does not appear in .spec.ReplicatedJobs", "UID": "0becc279-1e3a-48db-8328-b70dc007406a", "allowed": false}

And then the actual use case - a broker job in the jobset successfully finishing:

$ kubectl get -n flux-operator pods
NAME                                       READY   STATUS      RESTARTS   AGE
minicluster-flux-sample-broker-0-0-jmw2b   0/1     Completed   0          23s
minicluster-flux-sample-worker-0-0-nmnn8   0/1     Completed   0          23s
minicluster-flux-sample-worker-0-1-rv7gh   0/1     Completed   0          23s
minicluster-flux-sample-worker-0-2-48jp6   0/1     Completed   0          23s

You can see how we are using it here. We actually have a design for the operator now that the workers do exit when the broker leader exits, but this is nice because it's mapping that same logic into Kubernetes too.

I think once I've tested everything, the decision point will likely come down to being able to test this in a more production sense. The pros of this design are separation of the worker / broker logic into separate scripts. The cons are the longer names of the pods and (at least in this setup) what appears to be a bit of slowness sometimes. But I'm going to chock that up to my setup, and will assume when it's added proper it will be on par with the current objects in batch! The last thing to test is #136, and one thing I'm realizing is we would want to make sure that the label selector is transparent to be able to potentially apply it to other objects in the cluster (e.g., for the Flux Operator, a one off container service).