Show warning when there are no enabled entries or groups during Frontend or Factory reconfig/upgrade.
This is related to #22877.
There are no messages during Frontend or Factory reconfig/upgrade if ALL the groups or entries are disabled. At startup gives "No Entries are enabled. Exiting." if there are no entries, though.
It could be good to give a warning (or error?) if this is the case.
TODO: Either for the Frontend or Factory, check if the list of active groups/entries is empty or not. If so, warn the user