KEP-2033: KubeletInUserNamespace: promote to beta

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

Author: AkihiroSuda

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

@@ -9,6 +9,9 @@ stages:
   - stage: alpha
     defaultValue: false
     fromVersion: "1.22"
+  - stage: beta
+    defaultValue: true
+    fromVersion: "1.35"
 ---
 Enables support for running kubelet in a
 {{<glossary_tooltip text="user namespace" term_id="userns">}}.