Allow using flow option with TLS.

[Gh0u1L5]

Currently, the upstream xray project allows users to configure flow (e.g. xtls-rprx-vision) when using TLS, while v2raya lacks support for this. Please merge this PR to enhance the relevant functionality.

Example

{
    "protocol": "vless",
    "settings": {
        "vnext": [
            {
                "address": "<hostname>",
                "port": 443,
                "users": [
                    {
                        "id": "<client id>",
                        "encryption": "none",
                        "flow": "xtls-rprx-vision"
                    }
                ]
            }
        ]
    },
    "streamSettings": {
        "network": "tcp",
        "security": "tls"
    },
    "tag": "proxy"
}

[mzz2017]

Thanks for your great job!

[MarksonHon]

I have found this unknown text box had been the necessary one, but actually my server have no XTLS flow control