future-public: add set leverage request

config/bitunix-api.php

@@ -1,7 +1,9 @@
 <?php
 
-// config for Msr/LaravelBitunixApi
 return [
 
     'future_base_uri' => 'https://fapi.bitunix.com/',
+    'api_key' => env('BITUNIX_API_KEY'),
+    'api_secret' => env('BITUNIX_API_SECRET'),
+    'language' => 'en-US',
 ];