Export ProviderConfig to better support Responses API

[JakubK44]

Looking at exported types, ProviderConfig defined in nodejs/src/types.ts#L1226 is not one of them.

This appears to be the only way to access 'responses' API - by setting your ProviderConfig.wireApi := 'responses'. Currently, I have to duplicate the type locally. I suspect it's an oversight that it isn't exported.