What would you like to be added:

Initial implementation of KEP-77: Dynamically Sized Jobs via WorkloadSlices

Why is this needed:

This issue tracks the initial implementation of KEP-77, which introduces support for dynamically resizing jobs in Kueue through the concept of WorkloadSlices.

Completion requirements:

• Implement creation of WorkloadSlice objects upon scaling events (e.g., parallelism change for batchv1/Job).

  Add pod scheduling gates to defer scheduling until slice admission.

  Implement admission logic for WorkloadSlices.

  Support deactivation and garbage collection of preempted slices.

  Update quota and PodSetAssignments to reflect slice scaling.

  Annotate relationships between new slices and the slices they preempt.

  Add feature gate (WorkloadSlices) and opt-in annotation mechanism.

  Ensure compatibility with existing batch/v1.Job semantics.

  Unit and integration test coverage for scale-up and scale-down flows.
  To pick up a draggable item, press the space bar. While dragging, use the arrow keys to move the item. Press space again to drop the item in its new position, or press escape to cancel.

This enhancement requires the following artifacts:

• Design doc

  API change

  Docs update
  To pick up a draggable item, press the space bar. While dragging, use the arrow keys to move the item. Press space again to drop the item in its new position, or press escape to cancel.

The artifacts should be linked in subsequent comments.