backups: make part size configurable

src/storage/s3.js

@@ -121,7 +121,7 @@ function upload(apiConfig, backupFilePath, sourceStream, callback) {
         // s3.upload automatically does a multi-part upload. we set queueSize to 3 to reduce memory usage
         // uploader will buffer at most queueSize * partSize bytes into memory at any given time.
         // scaleway only supports 1000 parts per object (https://www.scaleway.com/en/docs/s3-multipart-upload/)
-        const partSize = apiConfig.provider === 'scaleway-objectstorage' ? 100 * 1024 * 1024 : 10 * 1024 * 1024;
+        const partSize = apiConfig.uploadPartSize || (apiConfig.provider === 'scaleway-objectstorage' ? 100 * 1024 * 1024 : 10 * 1024 * 1024);
 
         s3.upload(params, { partSize, queueSize: 3 }, function (error, data) {
             if (error) {