Update bqexport.js to use environment variable for GCS credentials instead of an empty object.

bqexport.js

@@ -9,7 +9,7 @@ const bigquery = new BigQuery({
 });
 const storage = new Storage({
   projectId: process.env.PROJECT_ID || 'fynd-jio-commerceml-prod',
-  credentials: {}
+  credentials: process.env.GCS_CREDENTIALS || {}
 });
 
 export const exportMergedJson = async (req, res) => {