server : Support listening on a unix socket

[p1-0tr]

Add support for listening on a unix socket in the example server.

To keep the change small, and avoid extending the set of cli flags I went with a slightly hacky way of passing the socket name to the server. I.e. if --host ends with .sock then create and listen on a unix socket, else listen on TCP. LMK if this is acceptable, or if it would be better to avoid overloading --host and create an additional cli flag?

[ngxson]

I think it also worth to mention this in arg.cpp

    add_opt(common_arg(
        {"--host"}, "HOST",
        string_format("ip address to listen, or bind to an UNIX socket if the address ends with .sock (default: %s)", params.hostname.c_str()),
        [](common_params & params, const std::string & value) {
            params.hostname = value;
        }
    ).set_examples({LLAMA_EXAMPLE_SERVER}).set_env("LLAMA_ARG_HOST"));

[p1-0tr]

I think it also worth to mention this in arg.cpp

    add_opt(common_arg(
        {"--host"}, "HOST",
        string_format("ip address to listen, or bind to an UNIX socket if the address ends with .sock (default: %s)", params.hostname.c_str()),
        [](common_params & params, const std::string & value) {
            params.hostname = value;
        }
    ).set_examples({LLAMA_EXAMPLE_SERVER}).set_env("LLAMA_ARG_HOST"));

Thanks, that's a great point :)