Add a setting not to forward status 103 on HTTP/1

We might not want to forward 103 response on H1. It's not a protocol violation but just a recommendation, so if we do this the behavior should be configurable.

> Note: For compatibility and security reasons, it is recommended to [only send HTTP 103 Early Hints responses over HTTP/2 or later](https://www.rfc-editor.org/rfc/rfc8297#section-3) unless the client is known to handle informational responses correctly.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/103