Add support for resolving HttpSession from Servlet applications

[flowersinthesand]

We got a feedback that a process to find javax.servlet.http.HttpSession from a socket is somewhat lengthy. Of course, it can be concise with the helper like this:

Server server = new DefaultServer();
server.onsocket(socket -> {
  HttpSessionResolver httpSessionResolver = new HttpSessionResolver();
  HttpSession httpSession = httpSessionResolver.resolve(socket);
  
  Set<String> tags = (Set<String>) httpSession.getAttribute("tags");
  socket.tags().addAll(tags);
});