Issue 50201 - nsIndexIDListScanLimit accepts any value
    
    Bug Description: Setting of nsIndexIDListScanLimit like
    'limit=2 limit=3' are detected and logged in error logs.
    But the invalid value is successfully applied in the config entry
    and the operation itself is successful.
    The impact is limited because the index will be used following
    idlistscanlimit rather than invalid definition nsIndexIDListScanLimit.
    
    Fix Description: Print the errors to the user when he tries to add
    or to modify index config entry with malformed values.
    Change tests accordingly.
    
    https://pagure.io/389-ds-base/issue/50201
    
    Reviewed by: mreynolds, tbordaz (Thanks!)