add: exercise answer for chapter 6 and 7

exercises/6/main.https.cpp

@@ -0,0 +1,18 @@
+//
+// main_https.cpp
+// web_server
+// created by changkun at changkun.de/modern-cpp
+//
+#include <iostream>
+#include "server.https.hpp"
+#include "handler.hpp"
+using namespace LabexWeb;
+
+int main() {
+    // HTTPS server runs in port 12345, enable 4 threads
+    // Use certificates for security
+    Server<HTTPS> server(12345, 4, "server.crt", "server.key");
+    std::cout << "Server starting at port: 12345" << std::endl;
+    start_server<Server<HTTPS>>(server);
+    return 0;
+}