TS String Enum for Stytch Token Type

I'd like to have a TS constant and a union type. Something like:

```ts
import {StytchToken, StytchTokenType} from "stytch";

const MAGIC_LINKS_TOKEN: StytchTokenType = StytchToken.Magic_Links; // "magic_links";
```

Docs:

https://stytch.com/docs/guides/dashboard/redirect-urls#structure

I don't want to use the `"magic_links"` string.