Remove postgres, add DB migrations

Removes PostgreSQL from the chart, and instead lets users install it separately. That way we can use the autoMigrate jobs from the Hydra and Kratos chart, so that doesn't have to be in this chart anymore either.

It also makes it possible to be sure that all systems are initialized once the post-install job runs that runs login database migrations and creates the admin user.

Also closes #124 (closed)