Add ignore_invalid_headers option for HTTP/1 server requests

[seanmonstar]

This proposes adding an option to hyper::server::conn::http1::Builder: ignore_invalid_headers(bool).

This could make use of the related option in httparse: https://docs.rs/httparse/latest/httparse/struct.ParserConfig.html#method.ignore_invalid_headers_in_requests

[GlenDC]

Resolved in #3824.