Allow Replacement of Pods in a Job when fully terminating

Currently, Jobs start replacement Pods as soon as previously created Pods are terminating (have a deletionTimestamp) or fail (phase=Failed). Terminating pods are currently counted as failed in the Job status. However, terminating pods are actually in a transitory state where they are neither active nor really fully terminated. This KEP proposes a new field for the Job API that allows for users to specify if they want replacement Pods as soon as the previous Pods are terminating (existing behavior) or only once the existing pods are fully terminated (new behavior).