fix(bulk-publish): declare module-level config variable in publish-assets.js

setConfig() assigned to `config` at module scope but the variable was
never declared, causing a ReferenceError on any cm:assets:publish run
that goes through the data-dir flow.

Author: aniket-shikhare-cstk

packages/contentstack-bulk-publish/src/producer/publish-assets.js

@@ -15,6 +15,7 @@ const { generateBulkPublishStatusUrl } = require('../util/generate-bulk-publish-
 const { resolveInQueueAssets, fetchScanStatusBatch, ASSET_SCAN_STATUS } = require('../util/asset-scan');
 
 const queue = getQueue();
+let config;
 let logFileName;
 let bulkPublishSet = [];
 let pendingAssetsForRetry = [];