Automatically add playlist metadata download item during migration

[Chaphasilor]

This enhances the user experience when adding tracks from playlists (as it shows which playlists the track is already part of), enables removing tracks from playlists using the playlist actions menu, and shows partially downloaded playlists in offline mode.

[Chaphasilor]

@Komodo5197 would you mind taking a look? I'll still have to test this out to see if it actually works, but maybe there's something that could be improved with the download code already ^^

[Komodo5197]

That seems about as I expected. I don't 100% remember how this migration script works when conducting the initial login, so definitely test that. Also, it might make more sense to chain the future so that the playlist download gets added before we start the repair, although this probably doesn't really matter.

[Chaphasilor]

From what I saw there's a hidden setting that is false by default and gets set to true after the migration, so it should be fine.

I thought about that, but wanted to prioritize the migration of existing downloads over the metadata. Is the download system even a proper FIFO queue?
Either way, I haven't decided on the final order yet. Might try out different approaches.