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/values.yaml

@@ -4,8 +4,10 @@ env:
   # Available options:
   # - `elasticsearch` (default)
   # - `infinity` (https://github.com/infiniflow/infinity)
+  # - `opensearch` (https://github.com/opensearch-project/OpenSearch)
   # DOC_ENGINE: elasticsearch
   DOC_ENGINE: infinity
+  # DOC_ENGINE: opensearch
 
   # The version of Elasticsearch.
   STACK_VERSION: "8.11.3"
@@ -13,6 +15,10 @@ env:
   # The password for Elasticsearch
   ELASTIC_PASSWORD: infini_rag_flow_helm
 
+  # The password for OpenSearch.
+  # At least one uppercase letter, one lowercase letter, one digit, and one special character
+  OPENSEARCH_PASSWORD: infini_rag_flow_OS_01
+
   # The password for MySQL
   MYSQL_PASSWORD: infini_rag_flow_helm
   # The database of the MySQL service to use
@@ -130,6 +136,22 @@ elasticsearch:
   service:
     type: ClusterIP
 
+opensearch:
+  image:
+    repository: opensearchproject/opensearch
+    tag: 2.19.1
+  storage:
+    className:
+    capacity: 20Gi
+  deployment:
+    strategy:
+    resources:
+      requests:
+        cpu: "4"
+        memory: "16Gi"
+  service:
+    type: ClusterIP
+
 minio:
   image:
     repository: quay.io/minio/minio