Set helm resource-policy to be keep (#7574)

Modified the chart to retain persistent volumes by default when the
chart is uninstalled, following established best practices in the Helm
community (e.g., Bitnami charts)

### What problem does this PR solve?

Previously, deleting the helm chart would automatically remove all
persistent data, which poses a risk of accidental data loss.

### Rationale

This change aligns with industry standards to safeguard data by
requiring explicit action to remove persistence, rather than making
deletion the default behavior.

### Impact: 

Users who intentionally want to remove persistent data will need to do
so manually or by setting appropriate flags during chart uninstallation.

### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

helm/templates/elasticsearch.yaml

 kind: PersistentVolumeClaim
 metadata:
   name: {{ include "ragflow.fullname" . }}-es-data
+  annotations:
+    "helm.sh/resource-policy": keep
   labels:
     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: elasticsearch

helm/templates/infinity.yaml

 kind: PersistentVolumeClaim
 metadata:
   name: {{ include "ragflow.fullname" . }}-infinity
+  annotations:
+    "helm.sh/resource-policy": keep
   labels:
     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: infinity

helm/templates/minio.yaml

 kind: PersistentVolumeClaim
 metadata:
   name: {{ include "ragflow.fullname" . }}-minio
+  annotations:
+    "helm.sh/resource-policy": keep
   labels:
     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: minio

helm/templates/mysql.yaml

 kind: PersistentVolumeClaim
 metadata:
   name: {{ include "ragflow.fullname" . }}-mysql
+  annotations:
+    "helm.sh/resource-policy": keep
   labels:
     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: mysql

helm/templates/redis.yaml

 kind: Service
 metadata:
   name: {{ include "ragflow.fullname" . }}-redis
+  annotations:
+    "helm.sh/resource-policy": keep
   labels:
     {{- include "ragflow.labels" . | nindent 4 }}
     app.kubernetes.io/component: redis