Make GCS delete concurrency configurable

services/filestore/app/js/GcsPersistor.js

@@ -209,9 +209,13 @@ async function deleteDirectory(bucketName, key) {
       .bucket(bucketName)
       .getFiles({ directory: key })
 
-    await asyncPool(50, files, async file => {
-      await deleteFile(bucketName, file.name)
-    })
+    await asyncPool(
+      settings.filestore.gcs.deleteConcurrency,
+      files,
+      async file => {
+        await deleteFile(bucketName, file.name)
+      }
+    )
   } catch (err) {
     const error = PersistorHelper.wrapError(
       err,

services/filestore/config/settings.defaults.coffee

@@ -42,6 +42,7 @@ settings =
 					projectId: process.env['GCS_PROJECT_ID']
 			unlockBeforeDelete: process.env['GCS_UNLOCK_BEFORE_DELETE'] == "true"  # unlock an event-based hold before deleting. default false
 			deletedBucketSuffix: process.env['GCS_DELETED_BUCKET_SUFFIX']          # if present, copy file to another bucket on delete. default null
+			deleteConcurrency: parseInt(process.env['GCS_DELETE_CONCURRENCY']) || 50
 
 		s3:
 			if process.env['AWS_ACCESS_KEY_ID']? or process.env['S3_BUCKET_CREDENTIALS']?