Re-check item on item detail update

ZBXNEXT-388 is a great feature that enables immediate checks for new items and discovery rules. However, there are situations when it's also desirable to do the same on item update.

For instance, if I change item key parameters for a Zabbix agent item or modify a formula for a calculated item I don't want to wait for the next interval. The same goes for items that are updated automatically by LLD. The immediate recheck should not be applied for all item parameters, just a few. For instance, there is no point in rechecking if only a description or storage period changed for the item.