Add SNI Proxy support

[robvanoostenrijk]

Pull request to add TLS (SNI) proxy support.

This allows using Wireproxy on local LAN to easily tunnel traffic through Wireguard based on DNS name.
By overriding the local DNS server to return the LAN IP of the Wireproxy instance, the traffic to that domain will be routed via the Wireguard tunnel.

1. Wireproxy receives traffic on the SNI proxy port (usually 443)
2. Wireproxy uses crypto/tls to do a read-only TLS connection to receive only the TLS client HELLO package.
3. The TLS client HELLO packet is inspected for the SNI extension. If found, the destination hostname is extracted.
4. Wireproxy connects to the destination hostname on port 443 (SNI extensions only carry hostname, not a target port)
5. Wireproxy then replays the initial TLS client HELLO package and establishes the TLS tunnel over TCP to the target
6. TCP connection tunnel is persistent until closed by client or server

Configuration Format:

[SNI]
BindAddress = 192.168.10.26:443

Example:

curl --resolve 'ifconfig.me:443:127.0.0.1' https://ifconfig.me/

This would return the Wireguard tunnel public IP through HTTPS connection with ifconfig.me