wrap account assets response in JSON object

app.py

@@ -37,6 +37,9 @@ class Asset:
         self.assetId = assetId
         self.balance = balance
 
+class Assets:
+    assets = []
+
 @app.get("/accounts/<string:accountId>/assets/")
 def get_account_assets(accountId): #TODO: add validation and error handling
 
@@ -45,10 +48,11 @@ def get_account_assets(accountId): #TODO: add validation and error handling
 
     iroha_response = net.send_query(query)
     data = iroha_response.account_assets_response.account_assets
-
-    response = []
+    
+    response = Assets()
+    response.assets = []
 
     for asset in data:
-        response.append(Asset(asset.asset_id, asset.balance))
+        response.assets.append(Asset(asset.asset_id, asset.balance))
 
     return jsonify(response)