Add button for sending test email

This allows for easily testing whether the provided email configuration is correct.

PR #20488.

src/webui/api/appcontroller.cpp

@@ -1107,6 +1107,11 @@ void AppController::defaultSavePathAction()
     setResult(BitTorrent::Session::instance()->savePath().toString());
 }
 
+void AppController::sendTestEmailAction()
+{
+    app()->sendTestEmail();
+}
+
 void AppController::networkInterfaceListAction()
 {
     QJsonArray ifaceList;

src/webui/api/appcontroller.h

@@ -48,6 +48,7 @@ private slots:
     void preferencesAction();
     void setPreferencesAction();
     void defaultSavePathAction();
+    void sendTestEmailAction();
 
     void networkInterfaceListAction();
     void networkInterfaceAddressListAction();