fix(MediaManager): use different HTTP streams for each variant

- So that the variant's transform stream don't block each other by the stream backpressure mechanism, or does not block others when exits writing before reading the whole file.

src/MediaManager.ts

@@ -1,3 +1,4 @@
+import fetch from 'node-fetch';
 import { Bucket, Storage, File } from '@google-cloud/storage';
 import { pipeline } from 'stream/promises';
 import prepareStream from './lib/prepareStream';
@@ -160,9 +161,11 @@ class MediaManager {
     // Must not await this promise because we still need to pipe body to another writable stream
     // for hash calculation below
     const uploadPromise = Promise.all(
-      variantSettings.map(({ transform, contentType }, i) =>
+      variantSettings.map(async ({ transform, contentType }, i) =>
         pipeline(
-          body,
+          // Initiate separate HTTP stream here, as each variant may consume the stream differently,
+          // or even ends before reading the whole file.
+          (await fetch(url)).body,
           transform,
           tempVariantFiles[i].createWriteStream({ contentType, gzip: 'auto' })
         )