add top_k for es full text search (#9963)

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

@@ -142,7 +142,7 @@ class ElasticSearchVector(BaseVector):
 
     def search_by_full_text(self, query: str, **kwargs: Any) -> list[Document]:
         query_str = {"match": {Field.CONTENT_KEY.value: query}}
-        results = self._client.search(index=self._collection_name, query=query_str)
+        results = self._client.search(index=self._collection_name, query=query_str, size=kwargs.get("top_k", 4))
         docs = []
         for hit in results["hits"]["hits"]:
             docs.append(