tyoescript-resolvers - Support customising mapper for List types

### Is your feature request related to a problem? Please describe.

`graphql-js` supports AsyncIterables for array query resolvers https://github.com/graphql/graphql-js/pull/2757

AFAICT, there is not a way to configure `graphql-codegen` to return AsyncIterables for array resolvers.

### Describe the solution you'd like

Either introduce something like an `ArrayField` type which supports everything `graphql-js` supports:

```ts
type ArrayField = T[] | AsyncIterable
```

(this might not be as generic as it could be, I haven't checked)

Or allow a way to define a mapper for arrays (maybe there is a way to do that already, I couldn't find any documentation for it).

### Describe alternatives you've considered

I could modify the generated code, or give up on codegen, or not use AsyncIterables.

### Any additional important details?

_No response_