[fetch-proxy] TLS/SSL issues due to host header not being updated

[itxch]

When proxying requests the Host header in the proxied Request isn't updated, this causes TLS issues due to host name not matching the certificate on the downstream server.

The fix would be very simple, we could simple add

proxyHeaders.set("Host", proxyUrl.host);

On line 61 here:

https://github.com/remix-run/remix/blob/8b557a421fe1aebaf7cb9903f96f20895bb7dd99/packages/fetch-proxy/src/lib/fetch-proxy.ts#L60-L65

If the team is open to this change I can raise a PR