Allow disabling rollback of GlobalSettings during deinstallation

GlobalSettingsOperation does try a 'reset' the setting during the uninstallation. This is guarded by a check whether the setting has been changed by other means after installation.

Some settings are ought not to be rolled back, and should be kept. This is the case e.g. for the Telemetry settings for Qt/QtCreator: After the user has made the choice, the setting should be arguably kept.

This could be achieved by a custom option to the operation.