Enable Playlist Radio on Spotify's Liked Songs tracks

I tested and created a IFTTT recipe for backing up Liked Songs' tracks : https://ifttt.com/applets/iMnNGt3V-backup-spotify-likes.

Despite the incorrect labelling "Saving a spotify track" means liking it, not "downloading to your device". So you can add it to another Spotify playlist.

To get historical likes, cmd-a / ctrl-a (or equivalent) all Liked Songs tracks and drag them into the backup playlist.

This enables playlist options such as Playlist Radio giving you similar songs to the ones in the backup playlist.