Add mix task to migrate the production database

lib/mix/tasks/music_library/prod/db_migrate.ex

@@ -0,0 +1,16 @@
+defmodule Mix.Tasks.MusicLibrary.Prod.DbMigrate do
+  use Mix.Task
+  @shortdoc "Run migrations on the production database"
+  @moduledoc """
+  Run migrations on the production database.
+
+  Requires the `flyctl` CLI to be installed and authenticated.
+  """
+
+  @impl Mix.Task
+  def run(_args) do
+    IO.puts("Running migrations on production database")
+
+    System.cmd("flyctl", ["ssh", "console", "--command", "bin/migrate"], into: IO.stream())
+  end
+end