AWS Lambda for performing video conversions via ffmpeg

API:

• GET /init to get a signed S3 URL to post a video to. Response is JSON with two keys, uploadUrl and key.
• POST your video to uploadUrl.
• GET /convert?key=<key from /init>&args=<ffmpeg args> will return JSON with url key with output

Relies upon https://github.com/serverlesspub/ffmpeg-aws-lambda-layer being deployed under the layer name ffmpeg (see https://github.com/mozilla/hubs-ops/blob/master/terraform/modules/speelycaptor/main.tf for relevant terraform)