top-level `casing` missing from Kit configuration

Casing was added in [drizzle-kit@0.25.0](https://github.com/drizzle-team/drizzle-orm/releases/tag/drizzle-kit%400.25.0)

```ts
import { defineConfig } from "drizzle-kit";

export default defineConfig({
dialect: "postgresql",
schema: "./schema.ts",
dbCredentials: {
url: "postgresql://postgres:password@localhost:5432/db",
},
casing: "snake_case", // NEW!
});
```
But is not mentioned in the configuration docs.

It is only mentioned in the [`introspect` section](https://orm.drizzle.team/docs/drizzle-config-file#introspect):

```ts
import { defineConfig } from "drizzle-kit";

export default defineConfig({
introspect: {
casing: "camel",
},
});
```