Transcode queuing concurrency is unbounded

[mojodna]

This means that if enough images (URLs, in my case) are submitted, lots of transcoding requests will be submitted simultaneously, eventually resulting in ECONNRESET and ECONNREFUSED.

The number of concurrent promises should be limited here:

oam-api/routes/uploads.js

Lines 527 to 547 in ed8af6e

	const transcoderPromisesAll =
	Promise.all([uploadPromise, insertImagesAll]).then((results) => {
	const sceneImageIds = results[1];
	const transcoderPromises = upload.scenes
	.reduce((accum, scene, sceneIndex) => {
	const imageIds = sceneImageIds[sceneIndex];
	const queuedImages = imageIds.map((imageId, imageIdIndex) => {
	const key = [uploadId, sceneIndex, imageId].join('/');
	const sourceUrl = scene.urls[imageIdIndex];
	return transcoder.queueImage(sourceUrl, key,
	`${config.apiEndpoint}/uploads/${uploadId}/${sceneIndex}/${imageId}`);
	});
	accum.push(...queuedImages);
	return accum;
	}, []);
	return Promise.all(transcoderPromises);
	});
	return transcoderPromisesAll.then(() => {
	return { upload: upload._id };
	});