fix: Add user agent for AzureCosmosDBMongoDBVectorStore (#1729)

Co-authored-by: yangqiao <yangqiao@microsoft.com>

.changeset/calm-windows-fry.md

+---
+"@llamaindex/azure": patch
+---
+
+Add UA for convenient statistics of usage

packages/providers/storage/azure/src/vectorStore/AzureCosmosDBMongoVectorStore.ts

@@ -106,7 +106,9 @@ export class AzureCosmosDBMongoDBVectorStore extends BaseVectorStore {
           "AzureCosmosDBMongoDBVectorStore client or connection string must be set.",
         );
       }
-      this.mongodbClient = new MongoClient(mongoUri);
+      this.mongodbClient = new MongoClient(mongoUri, {
+        appName: "LLAMAINDEX_JS",
+      });
     }
 
     this.dbName = init.dbName ?? "documentsDB";