Memory leak in the example

[romoloman]

In the first example the following handler generates a memory leak:

server->on("/upload", HTTP_POST, [](AsyncWebServerRequest *request) {
request->send(200);
}, handleUpload);

it should be written as

server->on("/upload", HTTP_POST, [](AsyncWebServerRequest *request) {
}, handleUpload);

Handling the response in the handleUpload function.

Otherwise request->send() clear the request while is still in use in the handleUpload() and then heap is never recovered....

[smford]

@romoloman are you able to raise a PR with your proposed fix please, it would be nice to include it in