* backend/api: refactor PlaylistId to PlaylistUid
* Add org_id to Get and Update playlist functions
Fix migration - no longer pad the uid; fix mysql syntax
The relevant tests are passing using postgres, mysql and the default sqllite backends, but there are a number of other failing tests when using postgres and myself so I'm not entirely confident with those results.
* fix bad query in GetPlaylistItem and add a test that would have caught the mistake in the first place. Reverted the playlist_uid column addition in playlist_item; it became unnecessary after this PR.
Added default value to the new UID column based on PR feedback.
* break this PRs migration into its own function
* Playlists: Update UI to use the updated API
Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>
