Fail fast if we cannot build indexes

[danielvegamyhre]

Fixes #263

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[danielvegamyhre]

cc @kannon92 @alculquicondor is this an appropriate way of handling the case where indexes cannot be built, or what is the typical approach here? I notice in the Kueue controller when setting up indexes, errors are only logged but program execution continues uninterrupted: https://github.com/kubernetes-sigs/kueue/blob/main/main.go#L178

However, as you can see in issue #263 in the case where indexes fail to build, JobSet controller is hitting a reconciliation error here and never starting the jobs due to these indexes not existing, so we need to handle this somehow. Perhaps if we get an error listing child jobs here, we should simply retry the call but without specifying an index (so it will be slower but at least work)?

[kannon92]

/lgtm