[coro_http_client][improve]Improve ssl

[qicosmos]

Why

set sni host name as default.

What is changing

Example

  std::string uri = "https://cn.bing.com";
  [[maybe_unused]] auto ec = client.init_ssl("cn.bing.com"); // set sni host name.
  auto data = co_await client.async_get(uri);