Update JobSuccessPolicy documentations for the beta graduation

Signed-off-by: Yuki Iwai <yuki.iwai.tz@gmail.com>

content/en/docs/concepts/workloads/controllers/job.md

@@ -598,7 +598,7 @@ Here is a manifest for a Job with `successPolicy`:
 In the example above, both `succeededIndexes` and `succeededCount` have been specified.
 Therefore, the job controller will mark the Job as succeeded and terminate the lingering Pods 
 when either of the specified indexes, 0, 2, or 3, succeed.
-The Job that meets the success policy gets the `SuccessCriteriaMet` condition. 
+The Job that meets the success policy gets the `SuccessCriteriaMet` condition with a `SuccessPolicy` reason.
 After the removal of the lingering Pods is issued, the Job gets the `Complete` condition.
 
 Note that the `succeededIndexes` is represented as intervals separated by a hyphen.

content/en/docs/reference/command-line-tools-reference/feature-gates/job-success-policy.md

@@ -10,5 +10,9 @@ stages:
   - stage: alpha
     defaultValue: false
     fromVersion: "1.30"
+    toVersion: "1.30"
+  - stage: beta
+    defaultValue: true
+    fromVersion: "1.31"
 ---
 Allow users to specify when a Job can be declared as succeeded based on the set of succeeded pods.