Add FeatureGate toggling implementation change since v1.33

Author: mochizuki875

content/en/docs/concepts/scheduling-eviction/topology-spread-constraints.md

@@ -168,6 +168,11 @@ your cluster. Those fields are:
   {{< note >}}
   The `matchLabelKeys` field is a beta-level field and enabled by default in 1.27. You can disable it by disabling the
   `MatchLabelKeysInPodTopologySpread` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/).
+
+  Before v1.33, kube-scheduler just internally handled `matchLabelKeys` before the calculation of scheduling results.
+  Since v1.33, merging selectors built from `matchLabelKeys` into `labelSelector` is enabled by default. 
+  You can disable it and revert to the previous behavior by disabling the `MatchLabelKeysInPodTopologySpreadSelectorMerge` 
+  [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) of kube-apiserver.  
   {{< /note >}}
 
 - **nodeAffinityPolicy** indicates how we will treat Pod's nodeAffinity/nodeSelector

content/en/docs/reference/command-line-tools-reference/feature-gates/MatchLabelKeysInPodTopologySpreadSelectorMerge.md

@@ -0,0 +1,14 @@
+---
+title: MatchLabelKeysInPodTopologySpreadSelectorMerge
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: beta
+    defaultValue: true
+    fromVersion: "1.33"
+---
+Enable merging of selectors built from `matchLabelKeys` into `labelSelector` of 
+[Pod topology spread constraints](/docs/concepts/scheduling-eviction/topology-spread-constraints/).