enable utls for websteps (#442)

This diff enables `websteps` to use uTLS for TLS parroting. It integrates the `oohttp.StdlibTransport` wrapper which uses the `ooni/oohttp` fork. `oohttp` supports TLS-like connections like `utls.Conn`.
As a prototype, the testhelper and `websteps` code now uses the `utls.HelloChrome_Auto` fingerprint, i.e. the simulated TLS fingerprint of the Google Chrome browser.

It is a further contribution for my GSoC project.

Reference issue: https://github.com/ooni/probe/issues/1733

internal/netxlite/tlshandshaker.go

@@ -135,6 +135,7 @@ func (c *UTLSConn) ConnectionState() tls.ConnectionState {
 		DidResume:                   uState.DidResume,
 		CipherSuite:                 uState.CipherSuite,
 		NegotiatedProtocol:          uState.NegotiatedProtocol,
+		NegotiatedProtocolIsMutual:  true,
 		ServerName:                  uState.ServerName,
 		PeerCertificates:            uState.PeerCertificates,
 		VerifiedChains:              uState.VerifiedChains,