Third Party Migrations

Alright, a long journey through the code later: confirmed that migrations only check app/Config/Autoload.php for namespaces. I updated MigrationRunner.php to use the Autoloader instead to check all initialized namespaces, which will include those sourced from Composer. I realize it is possible the original behavior was desired, but it seems odd to auto-autoload packages for all other purposes but still be forced to enter them manually in the config file if you want database support.
I'm open to discussion, here or GitHub: https://github.com/codeigniter4/CodeIgniter4/pull/1860