Move ErrorTracker to its own repo and file

Note that the SQlite adapter supports version 2 onwards.

priv/error_repo/migrations/20250101170610_add_error_tracker.exs

@@ -0,0 +1,6 @@
+defmodule MusicLibrary.Repo.Migrations.AddErrorTracker do
+  use Ecto.Migration
+  def up, do: ErrorTracker.Migration.up(version: 4)
+
+  def down, do: ErrorTracker.Migration.down(version: 2)
+end