TAS: reduce friction by defaulting the PodSet annotations

[mimowo]

What would you like to be added:

Allow scheduling workloads without TAS annotations (kueue.x-k8s.io/podset-required-topology or kueue.x-k8s.io/podset-preferred-topology) on every PodSet.

The idea is to default the annotations, but we need to decide where is the configuration.

Why is this needed:

Currently, users of TAS need to set annotations on every PodTemplate. While this gives control, it also creates friction and room for error, because users may forget to set the annotation. Also, most users want to use the "preferred" mode, and they don't need to control the topology level.

Completion requirements:

This enhancement requires the following artifacts:

• Design doc (KEP update)
• API change
• Docs update

The artifacts should be linked in subsequent comments.

[mimowo]

cc @mwielgus @mwysokin @tenzen-y

[mwysokin]

Maybe ResourceFlavor? Since it's usually related to the machine type and it can benefit only some of the machine types? Maybe the default could be kubernetes.io/hostname since it seems to give the best compact placement?