luci-app-ssr-plus: Added new SplitHTTP setting option in Xray version 1.8.16

[chika0801]

I've compiled the file myself and tested it on my router and it generates the Xray configuration file for the SplitHTTP parameters correctly and works fine.

    "streamSettings": {
      "network": "splithttp",
      "tlsSettings": {
        "allowInsecure": false,
        "fingerprint": "chrome",
        "serverName": "www.test123.top"
      },
      "splithttpSettings": {
        "host": "www.test123.top",
        "path": "/lovelive"
      },