Missing TS type definition for relay config

Jest offer users typed definitions for their config files:
```js
/** @type {import('jest').Config} */
const config = {
verbose: true,
};

module.exports = config;
```

As explained in their [docs](https://jestjs.io/docs/configuration), you can write your docs in JS and use JSDocs to get type inference. Another approach is to write the config file in TS and directly import the `Config` type.

Would the Relay team consider offering something similar? It would improve the DX when configuring the compiler. The current approach requires me to open the `relay-compiler` README to manually ensure I'm using the right options.