Improve custom attributes in Django itself.

Right now we have custom options at the Meta class, example `auto_refresh`:

```python
class RefreshModel(CrateModel):
field2 = models.TextField()

class Meta:
app_label = "test_app"
auto_refresh = True
```

But we are doing Metaclass shenanigans to a accomplish this due lo the lack of extensibility of the django internals.

More details in https://forum.djangoproject.com/t/allow-meta-class-to-have-extra-database-specific-options/40650/3

Start with the custom Meta option example in the issue and read the linked Django forum discussion about extra database-specific options. Define the Django extension point needed to support custom attributes without metaclass workarounds; done means the requested options are supported through Django itself.

Written by the indexing model from the issue text.