add option to customize and disable sni

[skbeh]

The code is adopted from https://github.com/SagerNet/sing-box.

Close #860.

[yeezylife]

   upstreams:
     - addr: "quic://dns.nextdns.io"
       insecure_skip_verify: true
       disable_sni: true
 ```
 请问你这个pr里加的功能 是不是要同时insecure_skip_verify: true和disable_sni: true 才能开启呀

[skbeh]

   upstreams:
     - addr: "quic://dns.nextdns.io"
       insecure_skip_verify: true
       disable_sni: true

请问你这个pr里加的功能 是不是要同时insecure_skip_verify: true和disable_sni: true 才能开启呀

The server name must be set to make the certificate verification work, otherwise insecure_skip_verify is required to be enabled.

[yeezylife]

   upstreams:
     - addr: "quic://dns.nextdns.io"
       server_name: dns.nextdns.io
       disable_sni: true

thanks for you reply, is this the correct server_name setting method? just fill it with the same url in addr?

[skbeh]

Yes, filling server_name with the server domain works most of the time.