feat(http): Skipping Middleware

[mathieucarbou]

• Allow to skip global server middleware on any handler
• Allow to access the catch-all handler to add middlewares on it

Solves: #49

I added an example showing how to use that: https://github.com/ESP32Async/ESPAsyncWebServer/blob/feat/skip-server-middleware/examples/SkipServerMiddleware/SkipServerMiddleware.ino

  // we apply auth middleware to the server globally
  server.addMiddleware(&basicAuth);

  // protected endpoint: requires basic authentication
  // curl -v -u admin:admin  http://192.168.4.1/
  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "Hello, world!");
  });

  // we skip all global middleware from the catchall handler
  server.catchAllHandler().skipServerMiddlewares();
  // we apply a specific middleware to the catchall handler only to log requests without a handler defined
  server.catchAllHandler().addMiddleware(&logging);

  // standard 404 handler: will display the request in the console i na curl-like style
  // curl -v -H "Foo: Bar"  http://192.168.4.1/foo
  server.onNotFound([](AsyncWebServerRequest *request) {
    request->send(404, "text/plain", "Not found");
  });

• you can skip the global middleware for any handler you want, including the catch-all
• you can add middleware to any handler, including catch-all.