Add OpenSearch support to Helm chart (#8921)

### What problem does this PR solve?

Adds OpenSearch support to the RAGFlow Helm chart based on
https://github.com/infiniflow/ragflow/pull/7140 and the existing
Elasticsearch support in the Helm chart.

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

helm/templates/elasticsearch-config.yaml

@@ -10,4 +10,8 @@ data:
   xpack.security.enabled: "true"
   xpack.security.http.ssl.enabled: "false"
   xpack.security.transport.ssl.enabled: "false"
+  cluster.routing.allocation.disk.watermark.low: 5gb
+  cluster.routing.allocation.disk.watermark.high: 3gb
+  cluster.routing.allocation.disk.watermark.flood_stage: 2gb
+  TZ: {{ .Values.env.TIMEZONE }}
 {{- end -}}