Drop the Pod TAS label in favor of an indexed field based on Workload

[mimowo]

What would you like to be added:

We would drop the use of the Pod TAS label which is used for filtering out the pods managed by TAS:

kueue/apis/kueue/v1alpha1/tas_types.go

Lines 57 to 61 in fd2519a

	// TASLabel is a label set on the Job's PodTemplate to indicate that the
	// PodSet is admitted using TopologyAwareScheduling, and all Pods created
	// from the Job's PodTemplate also have the label. For the Pod-based
	// integrations the label is added in webhook during the Pod creation.
	TASLabel = "kueue.x-k8s.io/tas"

This was requested as a cleanup in the comment: #3271 (comment)

However, if we hit roadblocks, we should revisit the proposal of dropping the label,

Why is this needed:

To avoid using labels which duplicate the information which is already present in the workload.

[mimowo]

cc @PBundyra @tenzen-y

[mimowo]

cc @mbobrovskyi