KEP-3619: Promote SupplementalGroupsPolicy to Beta in feature gate file

Author: everpeace

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

@@ -9,6 +9,10 @@ stages:
   - stage: alpha
     defaultValue: false
     fromVersion: "1.31"
+    toVersion: "1.32"
+  - stage: beta
+    defaultValue: true
+    fromVersion: "1.33"
 ---
 Enables support for fine-grained SupplementalGroups control.
 For more details, see [Configure fine-grained SupplementalGroups control for a Pod](/content/en/docs/tasks/configure-pod-container/security-context/#supplementalgroupspolicy).