Add possibility to setup custom request

[ricco24]

In some cases it can be useful to have opportunity setup custom request data.

E.g. I have custom proxy setup with another IP forwarding and need to change $remote_address before i send data to APM agent.

$transaction = $agent->getTransaction('myTransaction');
$request = $transaction->generateRequest();
$request['socket']['remote_address'] = $_SERVER['HTTP_X_REAL_IP'];
$transaction->setRequest($request);
$agent->send();

[philkra]

LGTM