[DOCS]: Update documentation for `drizzle.config.ts > migrations` section to include allowed prefix attribute values

### Enhancement hasn't been filed before.

- [x] I have verified this enhancement I'm about to request hasn't been suggested before.

### Describe the enhancement you want to request

The documentation for the [`drizzle.config.ts > migrations`](https://orm.drizzle.team/docs/drizzle-config-file#migrations) section is missing the allowed values for the `prefix` attribute in the migrations object type definition. The structure should be documented as:

```ts
{ table: string, schema: string; prefix: "index" | "timestamp" | "supabase" | "unix" | "none" }
```

The default value remains `{ table: "__drizzle_migrations", schema: "drizzle", prefix: "index" }`.

Please update the documentation to reflect the allowed values for the `prefix` attribute for better clarity on migrations configuration.