SoundCloud SET download feature.

[Godje]

Checklist

• I'm reporting a site feature request
• I've verified that I'm running youtube-dl version 2021.03.14
• I've searched the bugtracker for similar site feature requests including closed ones

Description

There is currently no functionality to download sets from SoundCloud.

Sets are usually prepared/selected by SoundCloud system, so they are different from a regular playlist. Example would be "The Upload" set, or "SoundCloud Weekly" set.
Both of these sets change either weekly, or slightly more often.

The sets are private by default, so would need a username login to soundcloud to download them.
Sets can be made public by a sure action inside on the SoundCloud website when visiting the set's page.

They are made for each user that is actively using the SoundCloud platform. The URLs for the sets I have mentioned are:

• https://soundcloud.com/discover/sets/weekly::username
• https://soundcloud.com/discover/sets/new-for-you::username

Currently when trying to download from those URLs, youtube-dl throws a 404 error whether I put in the -u part or not:

[soundcloud:set] discover/sets/new-for-you: Downloading JSON metadata
ERROR: Unable to download JSON metadata: HTTP Error 404: Not Found (caused by HTTPError()); please report this issue on https://yt-dl.org/bug