Add HTTPUpgrade transport

[xiaokangwang]

This is a reduced version of WebSocket transport that does not require actually implementing/using Websocket protocol itself. It sends http upgrade header to WebSocket and then use the upgraded http1.1 connection directly, cutting unnecessary overhead and protocol complexity of WebSocket.

This design is inspired by https://www.usenix.org/conference/foci20/presentation/frolov and based on WebTunnel Implementation.

Server Config Example, when hide behind nginx that deals with tls:

{
  "log": {
    "error": {
      "level": "Debug",
      "type": "Console"
    },
    "access": {
      "type": "None"
    }
  },
  "outbounds": [
    {
      "protocol": "freedom"
    }
  ],
  "inbounds": [
    {
      "protocol": "vmess",
      "settings": {
        "users": [
          "1234"
        ]
      },
      "listen": "127.0.0.1",
      "port": 1234,
      "streamSettings": {
        "transport": "httpupgrade",
        "transportSettings": {
          "host": "XXXX",
          "path": "XXXX"
        }
      }
    }
  ]
}

Client Config Example:

{
  "log": {
    "error": {
      "level": "Debug",
      "type": "Console"
    },
    "access": {
      "type": "None"
    }
  },
  "outbounds": [
    {
      "protocol": "vmess",
      "settings": {
        "port": 443,
        "uuid": "XXXX",
        "address": "XXXX"
      },
      "streamSettings": {
        "transport": "httpupgrade",
        "transportSettings": {
          "host": "XXXX",
          "path": "XXXX"
        },
        "security": "tls",
        "securitySettings": {
          "serverName": "XXXX",
          "allowInsecure": false,
          "nextProtocol": [
            "http/1.1"
          ]
        }
      }
    }
  ],
  "inbounds": [
    {
      "protocol": "socks",
      "settings": {
        "udpEnabled": true,
        "address": "127.0.0.1",
        "packetEncoding": "Packet"
      },
      "port": 1080
    }
  ]
}

[codecov-commenter]

Codecov Report

Attention: 125 lines in your changes are missing coverage. Please review.

Comparison is base (cb84b28) 37.79% compared to head (1eefcd3) 37.68%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2727      +/-   ##
==========================================
- Coverage   37.79%   37.68%   -0.12%     
==========================================
  Files         654      659       +5     
  Lines       38723    38873     +150     
==========================================
+ Hits        14636    14649      +13     
- Misses      22477    22607     +130     
- Partials     1610     1617       +7     

Files	Coverage Δ
transport/internet/httpupgrade/errors.generated.go	0.00% <0.00%> (ø)
transport/internet/httpupgrade/httpupgrade.go	25.00% <25.00%> (ø)
transport/internet/httpupgrade/dialer.go	6.66% <6.66%> (ø)
transport/internet/httpupgrade/config.pb.go	30.76% <30.76%> (ø)
transport/internet/httpupgrade/hub.go	4.08% <4.08%> (ø)

... and 7 files with indirect coverage changes

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[freedmanop]

客户端照你的写法不能用，可以说详细一点吗

[DDCHlsq]

实测能用，延迟比 gRPC 传输略高，比 ws 低，但是速度是 gRPC 的 3 倍（GIA线路，本地千兆测试），

[CrazyBoyFeng]

@freedmanop 我估计你是用 v4 的模式载入的配置文件。httpupgrade 目前只提供了 v5 格式的配置接入：

./v2ray run -c config.json -format jsonv5