Auto discover models recursively

Problem

For now, we need to specify explicitly from which modules Tortoise finds models, but not submodules, recursively.

In the example below, Tortoise loads models from models module, but not models.users or models.users.customers.

tortoise_config = {
    "connections": {"default": DATABASE_URI},
    "apps": {
        "models": {
            "models": ["models", "aerich.models"]
        }
    },
}

Proposed Solutions

1. Support "models": ["models.*", "aerich.models"] syntax.
2. Add another flag to discover models recursively.

Start at the configuration handling for the apps.models.models entries shown in the example, and trace how a module is currently discovered. Resolve whether wildcard syntax or a recursive-discovery flag is the intended API, then define behavior for nested modules such as models.users.customers. Done means the selected API discovers models recursively while preserving explicit entries such as aerich.models.