Manager: Fix UUID generation for manager config headers

Fix different UUIDs generating depending on the whether the path
is absolute or relative; they now always match the ones saved
inside .cfg files
Also reduce some code duplication

src/qt/qt_util.hpp

@@ -18,6 +18,7 @@ QScreen *screenOfWidget(QWidget *widget);
 void setWin11RoundedCorners(WId hwnd, bool enable);
 #endif
 QString currentUuid();
+QString generateUuid(const QString &path);
 void storeCurrentUuid();
 bool compareUuid();
 void generateNewMacAdresses();