Merge pull request #49351 from tengqm/fg-btree-132

Add feature gate BtreeWatchCache for v1.32.

Author: k8s-ci-robot

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

@@ -0,0 +1,16 @@
+---
+title: BtreeWatchCache
+content_type: feature_gate
+
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: beta 
+    defaultValue: true
+    fromVersion: "1.32"
+---
+When enabled, the API server will replace the legacy HashMap-based _watch cache_
+with a BTree-based implementation. This replacement may bring performance improvements.
+