Fix EZP-22113: Adding items to block is not published immediately

Link: https://jira.ez.no/browse/EZP-22113

## Description
If a user updates a block and quickly (less than 5 sec) sends the object for publishing, the block won't be taking into account. The object will have to be republished (manually or by the cronjob) to display the block.

## Proposed fix
The safety time can be configured. It can be used on very fast machines and should not introduce regression for users not experiencing this issue.

## Tests
Manual tests