Support for Transparent Proxy

I wanted to see if the transparent proxy feature is added to NITM. Basically, in windows firewall driver, the traffic can be directed to a transparent proxy (with intact dest IP and port). To support that, I was thinking of the following changes:

1. Add proxy/TransparentProxyHandler which adds tlsFrontendHandler in the pipeline (if TLS is not detected, it auto switches to HTTP1 anyway).
2. Modify Http1FrontendHandler to essentially replicate handleHttpProxyConnection. We are duplicating the request anyway.

        if (master.config().getProxyMode() == ProxyMode.HTTP && !tunneled) {
            if (request.method() == HttpMethod.CONNECT) {
                handleTunnelProxyConnection(ctx, request);
            } else {
                handleHttpProxyConnection(ctx, request);
            }
        } else if (master.config().getProxyMode() == ProxyMode.TRANSPARENT) {
            handleHttpProxyConnection(ctx, request);
        } else {
            LOGGER.debug("{} : {}", connectionContext, request);
            connectionContext.serverChannel().writeAndFlush(ReferenceCountUtil.retain(request));
        }

1. Add caching of client certificates that are generated for performance.

Please let me know your thoughts on this.

[abbasvalliani]

Thanks. Testing it now and will submit a PR shortly. BTW, fantastic work on the proxy.

[chhsiao90]

It was just released, it might takes hours to sync to the maven central, maybe you can check it later!