keps: add Graceful Deletion for Custom Resources kep

This KEP proposes adding support for graceful deletion to Custom Resources (CRs)
by honoring the `--grace-period` flag (and `DeleteOptions.GracePeriodSeconds`)
during deletion operations. Currently, when users delete a Custom Resource with
a specified grace period, the value is ignored, leading to unexpected behavior
for controllers and operators that rely on finalizers and graceful shutdown logic.

This enhancement will ensure that when a Custom Resource is deleted with a grace
period, the `metadata.deletionGracePeriodSeconds` field is properly set, allowing
finalizers to observe this value and implement appropriate graceful shutdown
behavior.

This KEP proposes implementing this as stable behavior without a feature gate,
as the change is purely additive, backward compatible, and poses minimal risk.

Signed-off-by: Daniel Sionov <[email protected]>

Author: dasionov