add ability to set no deletion for discovery rule lost resources.

i have 2 custom discovery rules whose items will most of the time show not discovered as these items are only present for short time periods.  the items created are for watching the size of files (based on similar names) and IP connections when over a specific count.

the issue is that i know that these items should not be deleted if reviewing hosts but the warning stating that the item will be auto deleted could cause another admin to think these items can be safely deleted.  plus, i know that the items are only available for brief times but cannot be guaranteed when on any given day.