qml: add test harness for onboarding qml tests

Author: Johnny Carlson

src/qml/test/onboardingtests.cpp

@@ -0,0 +1,2 @@
+#include <QtQuickTest>
+QUICK_TEST_MAIN(onboarding)

src/qml/test/onboardingtests.h

@@ -0,0 +1,19 @@
+// Copyright (c) 2014-2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <QObject>
+#include <QQmlEngine>
+
+class Setup : public QObject
+{
+    Q_OBJECT
+
+public:
+    Setup(); 
+    ~Setup() = default;
+
+public Q_SLOTS:
+    void qmlEngineAvailable(QQmlEngine * engine); 
+};
+