Update how API key are created and issued

Currently, we have the `ApiUser` model from `packagedb` (https://github.com/nexB/purldb/blob/main/packagedb/models.py#L1290) where we use the `create_api_user` management command (https://github.com/nexB/purldb/blob/main/packagedb/management/commands/create_api_user.py) to create user accounts. This is different than how we create users for scancode.io, where the `create-user` command uses the user model from `django.contrib.auth` (https://github.com/nexB/scancode.io/blob/main/scanpipe/management/commands/create-user.py).

We should create users in the same way in purldb.

In the situation where we have a companion matchcode instance that accesses the purldb database, we can route the `auth` and `auth_user` django apps to the purldb and have matchcode instance have the same users as the purldb instance.