KEP-4832: add SchedulerAsyncPreemption to the doc (#48407)

* KEP-4832: add SchedulerAsyncPreemption to the doc

* fix: address reviews

Author: sanposhiho

content/en/docs/reference/command-line-tools-reference/feature-gates/scheduler-async-preemption.md

@@ -0,0 +1,16 @@
+---
+title: SchedulerAsyncPreemption
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.32"
+---
+
+Enable running some expensive operations within the scheduler, associated with
+[preemption](/docs/concepts/scheduling-eviction/pod-priority-preemption/), asynchronously.
+Asynchronous processing of preemption improves overall Pod scheduling latency.