Webtransport transport should use quic-go's EarlyConnection

[MarcoPolo]

Right now we are adding an extra roundtrip to WebTransport connections because the server waits for the TLS handshake to complete before sending the h3 SettingsFrame.

This isn't necessary, and doesn't give us anything useful. In WebTransport we are authenticating the client with a Noise handshake, so it's okay to send the SettingsFrame to an unauthenticated client (it would also be okay otherwise as well, since by the time we have the client's h3 Settings frame we've already finished our handshake).

The implementation of this is a bit complicated because of the QUIC connection reuse code. The simplest thing is likely to only use .ListenEarly and wait for the handshake to complete in the case of non-Webtransport transports.

[sukunrt]

A Connection establishment RTT test would've helped prevent this:

libp2p/test-plans#52