Add Redis data retention policy config options (#9080)

### What problem does this PR solve?

Adds configuration options to the RAGFlow Helm chart to set the Redis
data retention policies. By default this feature is disabled to maintain
support with older Kubernetes versions.

https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#persistentvolumeclaim-retention

### Type of change

- [X] New Feature (non-breaking change which adds functionality)

helm/templates/redis.yaml

@@ -64,6 +64,15 @@ spec:
             {{- . | toYaml | nindent 12 }}
           {{- end }}
   {{- if .Values.redis.persistence.enabled }}
+  {{- with .Values.redis.persistence.retentionPolicy }}
+  persistentVolumeClaimRetentionPolicy:
+    {{- with .whenDeleted }}
+    whenDeleted: {{ . }}
+    {{- end }}
+    {{- with .whenScaled }}
+    whenScaled: {{ . }}
+    {{- end }}
+  {{- end }}
   volumeClaimTemplates:
     - metadata:
         name: redis-data

helm/values.yaml

@@ -187,6 +187,11 @@ redis:
     capacity: 5Gi
   persistence:
     enabled: true
+    # Set's the retention policy for the persistent storage (only available in k8s 1.32 or later)
+    # https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#persistentvolumeclaim-retention
+    # retentionPolicy:
+      # whenDeleted: Delete
+      # whenScaled: Delete
   deployment:
     strategy:
     resources: