Added example that shows how to sync subscriptions

[pSpitzner]

I follow some playlists that are updated regularly on spotify via tidal.
This might be a cool example and good use-case to show.

I was tweaking this a bit more, and after the refactor it works quite well.
If we fix some of the open issues (retry logic) the code should also be much shorter.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[pSpitzner]

Since our backend changes, this has become much cleaner. Running fine now on my tests.

I also started on workflows to run it on github, but the token reneweal and upload logic warrants a 4 eye check (not commiteed yet, cos, well, ugly)

[semohr]

We should clean up the terminology around sync, migrate, and subscribe. Right now, it’s not always clear what we mean when we use these terms. We should formalize the definitions and document them.

Here’s a proposal that feels consistent to me:

• Subscription: Keeping one (or multiple) playlists coupled to another playlist in a one-directional way (i.e., changes flow from source to subscriber only).
• Sync: Keeping multiple playlists synchronized, meaning changes in any of them are reflected across all linked playlists (bi-directional or multi-directional).
• Migration: A one-time copy of a playlist with no ongoing relationship between source and target.
• into Sink: Putting tracks into a playlist without deleting previously added tracks

[semohr]

Do you think we could make this example more generic?

Ideally, given any source playlist, it should be possible to attach multiple subscriber playlists and keep them updated by simply re-triggering the script (or by defining a polling interval). Independent of service specifics.

Would be a good intermediate step for us before we start to work on the fully synchronized playlists example.

Should also allow us to futher evaluate our abstraction 🙃