allow mp4 downloads from hls edge server

[joschahenningsen]

Motivation and Context

Currently we have two versions of the same video:

• the hls stream intended for streaming
• the mp4 file intended for downloads

This is unneccesarry and a huge waste of resources. This PR allows the edge server to deliver a hls stream by combining the segments into one mp4.

Steps for testing:

• start TUM-Live, a worker and the vod service
• upload a vod
• go to admin panel and download vod from edge server

[github-actions]

Your Testserver will be ready at https://931.test.live.mm.rbg.tum.de in a few minutes.

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