backend: add PlaylistUIDs to Playlist; remove playlist IDs from API (#49609)

* 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>

pkg/services/sqlstore/migrations/migrations.go

@@ -91,6 +91,7 @@ func (*OSSMigrations) AddMigration(mg *Migrator) {
 	accesscontrol.AddManagedPermissionsMigration(mg, accesscontrol.ManagedPermissionsMigrationID)
 	accesscontrol.AddManagedFolderAlertActionsMigration(mg)
 	accesscontrol.AddActionNameMigrator(mg)
+	addPlaylistUIDMigration(mg)
 }
 
 func addMigrationLogMigrations(mg *Migrator) {