add the index field for elasticsearch (#10592)

Author: JohnJyong

api/core/rag/datasource/vdb/elasticsearch/elasticsearch_vector.py

@@ -178,6 +178,7 @@ def create_collection(
                         Field.VECTOR.value: {  # Make sure the dimension is correct here
                             "type": "dense_vector",
                             "dims": dim,
+                            "index": True,
                             "similarity": "cosine",
                         },
                         Field.METADATA_KEY.value: {