Add websocket support, Add TLS ECH domain fronting, Add agent checkin…

[virusvfv]

1. Add websocket support. Now agent can connect via CDN (etc Clouflare)
2. Add TLS1.3 ECH (encrypted client helo). Now C2 domain will not be visible in EDR/Proxies/etc. Additionally yu can set front domain (ex. microsoft.com to be in TLS SNI)
3. Add agent auto deleting when agent is lost and its yamux session is closed

P.S Because Cloudflare GO fork is required for compiling, I think that it should be cloned to separate branch (ex websocket)

[virusvfv]

See full article about Tls 1.3 ECH DomainFronting (on russian):
https://habr.com/ru/post/702420/

[nicocha30]

Thanks for the PR! As Cloudflare GO is required for compiling, I will not merge this PR. Please, ping me when ECH is supported on official Go! 😉

[AdnaneKhan]

@virusvfv I was playing around with your changes (awesome TTP btw!!) and ran into a crash on the proxy side when trying to make UDP requests. Any tips on where I should start looking to fix this?

goroutine 50 [running]:                             
github.com/nicocha30/gvisor-ligolo/pkg/tcpip/stack.
Buffer).headerView(0xc00006bc20?, 0x891650?)               
        /root/go/pkg/mod/github.com/nicocha30/gvisor-ligolo
@v0.0.0-20220722133119-738ce3d82e3a/pkg/tcpip/stack/packet_
buffer.go:356 +0x145                                       
github.com/nicocha30/gvisor-ligolo/pkg/tcpip/stack.PacketHe
ader.Slice({0xc00017e8c0?, 0x400000?})                     
        /root/go/pkg/mod/github.com/nicocha30/gvisor-ligolo
@v0.0.0-20220722133119-738ce3d82e3a/pkg/tcpip/stack/packet_
buffer.go:492 +0x25                                        
github.com/nicocha30/gvisor-ligolo/pkg/tcpip/stack.(*Packet
Buffer).Network(0xc00011f800?)                             
        /root/go/pkg/mod/github.com/nicocha30/gvisor-ligolo
@v0.0.0-20220722133119-738ce3d82e3a/pkg/tcpip/stack/packet_
buffer.go:403 +0x5d                                        
github.com/nicocha30/gvisor-ligolo/pkg/tcpip/transport/udp.
(*ForwarderRequest).CreateEndpoint(0xc00024bb00, 0x47ea5e?)
        /root/go/pkg/mod/github.com/nicocha30/gvisor-ligolo
@v0.0.0-20220722133119-738ce3d82e3a/pkg/tcpip/transport/udp
/forwarder.go:77 +0xdc                                     
ligolo-ng/pkg/proxy/netstack.HandlePacket.func1()          
        /ligolo_custom/build/pkg/proxy/netstack/handlers.go
:142 +0x45b                                                
created by ligolo-ng/pkg/proxy/netstack.HandlePacket       
        /ligolo_custom/build/pkg/proxy/netstack/handlers.go
:129 +0x885